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[Stkrkotvte  Edition.] 


HUMAN    PHYSIOLOGY, 


FOPv.    THE    USE    OF 


ELEMENTARY   SCHOOLS, 


BY  CHARLES  A.  LEE.  M.  D., 

2^         XATE   PROFESSOR   OP   MATERIA   MEDICA   AND    MEDICAL    JURISPRUDENCE,    IN 
THE    UNIVERSITY   OF    THE    CITY    OF   NEW    YORK. 


"  The  proper  study  of  Mankind  is  Man. 


SECOND   EDITION. 


NEW     Y  O  R^:^<o^O 

PUBLISHED   BY    THE    AMERICAN    Cjtjiljp   ' 


128  FULTON  s^rj:et.    Ol**^^*^     '         / 


/J/ 


Entered,  according  to  Act  of  Congress,  in  the  year  1838, 

By  J.  Orville  Taylor, 
In  the  Clerk's  office  of  the  District  Court  of  the  Southern 

District  of  New  York. 


^ 


Stereotyped  bv  Smith  &  Wright,  216  William  St.  N.  Y. 


J^        Piercy  &  Eeed,  Printers,  9  Spruce  St.  N.  York. 


&i  jfX3^ 


r 


^:; 


TO 

CHARLES  ANTHON,  L.  L.  D. 

JAY     PROFESSOR     OF     LANGUAGES 

IN  Columbia  College, 

THIS     humble     essay, 

IS    BY    PERMISSION, 

GRATEFULLY     INSCRIBED, 

JN   TESTIMONY   OF   PROFOUND   RESPECT. 


PREFACE  TO  THE  SECOND  EDITION. 


In  presenting  to  the  public  the  present  stereotype  edi- 
tion of  this  work,  it  is  proper  to  state,  that  no  labor  or 
expense  has  been  spared  to  render  it  still  more  v/orthy 
of  the  kind  approbation  with  which  it  has  been  received. 
A  large  proportion  of  it  has  been  entirely  re-written, 
many  corrections  have  been  made,  and  numerous  and 
highly  valuable  illustrations  introduced ;  these  improve- 
ments, together  with  the  questions  at  the  end  of  each 
chapter,  cannot  but  render  the  work  better  adapted  to 
^e  objects  for  which  it  was  written. 

The  author  flatters  himself  that  this  treatise  will  be 
found  to  contain  the  substance-  of  what  is  yet  known  on 
the  subject  of  Human  Physiology,  and  most  that  is 
valuable,  which  is  scattered  through  many  learned  and 
ponderous  volumes.  In  preparing  it,  more  than  fifty 
different  works  have  been  consulted,  from  all  of  which 
the  author  has  freely  taken  whatever  he  found  adapted 
to  his  purpose.  Originahty  has  not  been  aimed  at,  as  it 
was  precluded  by  the  very  nature  of  the  subject ;  in- 
deed it  would  have  been  unsuited  to  the  object  in  view; 


VIU  PREFACE. 

From  the  rapid  sale  of  the  first  edition,  and  the  nu- 
merous orders  for  the  work  from  all  parts  of  the  United 
States,  it  may  safely  be  concluded,  that  Physiology  is 
henceforth  to  be  one  of  the  common  branches  of  know- 
ledge taught  in  our  schools,  academies,  and  other  semi- 
naries   of    learning.      Indeed    it    is    remarkable,    that 
sciences,  so  closely  connected   with  the  health  and  hap- 
piness of  our  race,  as  those  which  teach  us  the  structure 
and  functions  of  the  human  body,  should  so  long  have 
been   confined    to    those    who    intend   to   pursue    the 
practice  of  medicine  and  surgery  as  a  profession,  espe- 
cially when  the  practical  application  of  such  knowledge 
is  daily  and  hourly  of  the  utmost  importance  to  every 
individual,  connected  as  it  is,  with  the  preservation  of 
health  and  of  life.     That  such  studies  are  not  above  the 
comprehension  of  children  I  can  testify,  not  only  from 
my  own  observation,  but  from  the  experience  of  numer- 
ous teachers,  such  as  those  whose  names  are  appended 
to  the  testimonials,  on  the  first  pages  of  this  work.     If 
this  is  not  sufficient,  I  have  to  commend  to  the  attention 
of  the  reader,  the  following  extract  from  a  lecture  of 
Mr.  George  Combe,  the  distinguished  phrenologist  of 
Edinburgh,  which  he  was  so  kind  as  to  communicate  to 
me  by  letter  : 

"  I  take  the  hberty  to  urge  very  earnestly  on  your  at- 
tention, not  only  the  advantage,  but  the  necessity  of  in- 
troducing instruction  in  anatomy  and  physiology  into 
popular  education.  The  great  laws  of  health  cannot  be 
understood,  nor  can  their  importance  be  appreciated 


PREFACE.  IX 

without  this  knowledge.  I  do  not  mean  that  you  should 
teach  your  children  all  the  minute  details  of  these 
sciences,  which  would  be  necessary  if  you  intended 
them  for  the  ;m:actice  of  medicine  and  surgery :  all  I 
desire  is,  that  the  structure  of  the  leading  organs  of  the 
body  should  be  explained  so  far  as  to  render  the  func- 
tions of  them  intelligible,  and  that  on  this  knowledge 
should  be  founded  a  clear  and  practical  elucidation  of 
the  laws  of  health.  I  can  certify,  from  observation, 
that  this  instruction  may  be  communicated  to  children 
of  ten  years  of  age,  and  upwards,  with  great  success. 
The  structure  addresses  their  observing  faculties,  and 
an  explanation  of  the  functions  is  as  interesting  to  them 
as  a  romantic  story." 

In  treating  of  physiological  subjects,  I  have  unavoid- 
ably employed  some  technical  terms,  but  only  in  cases 
where  there  was  an  evident  advantage  attending 
their  use;  but  in  all  such  cases  the  exact  meaning 
of  the  term  has  been  assigned  it.  This  explanation 
saves  the  necessity  of  a  glossary,  which  was  appended 
to  the  first  edition,  and  it  is,  therefore,  omitted  in  the 
present. 

It  will  be  perceived  that  the  present  edition  contains 
more  anatomy  than  the  former.  This  has  arisen  from 
the  full  conviction,  that  in  order  to  understand  the 
functions  of  an  organ,  its  structure  must  first  be  learn- 
ed. To  aid  in  the  accomplishment  of  this  object,  nu- 
merous well-executed  wood  cuts  have  been  introduced, 
alike  creditable  to  the  artist  and  useful  to  the  learner. 


X  PREFACE. 

The  work  is,  therefore,  presented  to  the  public  in  its 
present  shape,  with  the  hope  and  belief,  that  it  will 
subserve  the  cause  of  human  knowledge  and  happi- 
ness. 

New  York,  April,  1839. 


CONTENTS. 


Page. 

Chap.  I. — Organic  and  Inorganic  Bodies         ....  13 

Chap.  II. — Division  of  the  Animal  Kingdom       »        .         .  20 

Chap.  III. — Structure  of  the  Human  Body     .         .         .         .  24 

Chap.  IV. — Structure  of  the  Human  Body  continued         .         .  39 

Chap.  V. — Chemistry  of  the  Human  Body             ...  56 

Chap.  VI.— The  Human  Skeleton             .         .         .         .         .  63 

Chap.  VII. — Properties  of  Animal  Bodies     .         ,         .         •  95 

Chap.  VIII. — Relation  of  Animal  Bodies  to  Heat,  Light,  and 

Electricity        , .         .  105 

Chap.  IX.— The  Nervous  System 110 

Chap.  X. — Intellectual  and  Moral  Faculties             .         .         .  123 

Chap.  XI. — The  Spinal  Marrow  and  its  Functions               .  135 

Chap.  XII. — The  Nerves  and  their  Functions          .         .         .  144 

Chap.  XIII. — The  five  Senses — Sense  of  Touch           .         .     ^  156 

Chap.  XIV.— Sense  of  Taste 167 

Chap.  XV.— Sense  of  Smell        ......  177 

Chap.  XVI.— Sense  of  Sight            .         .        .         .         .         .  190 

Chap.  XVII.— Sense  of  Hearing 225 

Chap.  XVIII.— Respiration        .             237 

Chap.  XIX.— The  Circulation  of  the  Blood         ....  256 

Chap.  XX. — Nutritive  Functions — ^Digestion          .         .         .  274 

Chap.  XXI.— Secretion 286 

Chap.  XXII.— Absorption       .         ...         .         .         .  292 

Chap.  XXIII.— Nutrition 298 

Chap.  XXIV.— Animal  Heat         .        .         .         .        •         .  304 

Chap.  XXV.— The  Voice  .         .        .         .         .         .         .312 

Chap.  XXVI. — Locomotion,  and  its  Organs,         .         .         .  319 

Chap.  XXVII.— The  Teeth*             326 

Chap.  XXXIII.— Sleep  and  Death 331 

*  Written  by  Solomon  Brown,  A.  M.  Scientific  and  Practical  Dentist  of  this  city. 


<V      OF  THE      -^^'^ 


[^ 


HUMAN    PHYSIOLOGY. 


CHAPTER  r. 

DEFINITION  ; — ORGANIC  AND  INORGANIC  BODIES. 

1.  Physiology  is  "  the  science  of  life,'*  or  that  branch 
of  knowledge  which  explains  the  uses  of  the  various  organs 
of  living  beings.  VegetaUe  physiology  treats  of  the  func- 
tions of  plants  ;  and  Comparative  physiology^  of  those  of  the 
inferior  orders  of  animals  ;  while  Human  'physiology  treats 
exclusively  of  man. 

2.  The  kingdom  of  nature  embraces  three  great  classes, 
ANIMALS,  VEGETABLES,  and  MINERALS.  Accordiug  to  a  more 
scientific  arrangement,  it  is  composed  of  organic  and  inoV' 
ganic  bodies.  By  organic  bodies,  we  mean  those  which 
possess  organs  or  instruments  for  the  performance  of  certain 
functions  ;  and  by  inorganic,  those  which  do  not.  It  is  by 
a  knowledge  of  these  works  of  God,  that  we  derive  our  ideas 
of  his  power,  wisdom,  and  goodness. 

3.  Organized  bodies  are  divided  into  two  great  classes, 
animals  and  vegetables  ;  which  differ  from  inorganic  matter 
in  several  respects,  the  most  important  of  which  are  the 
following  : — 

4.  Organized  bodies  have  a  certain  determinate  form, 
peculiar  to  the  species  to  which  they  belong.  Every  species 
of  plant  or  animal  may  be  known  by  its  external  shape  ;  as 

2 


14  PHYSIOLOGY. 

a  horse,  a  cow,  a  tree,  or  a  rose.  They  differ  so  much  from 
all  other  kinds,  that  we  are  seldom  in  danger  of  mistaking 
them.  This  will  not  apply  to  inorganic  bodies,  except, 
perhaps,  to  a  few  minerals  which  crystallize  in  a  certain 
shape. 

5.  In  organized  bodies,  we  find  the  parts  of  which  they 
are  composed,  distinguished  by  round  or  oval  forms  ;  as  the 
body  and  leaves  of  trees  ;  the  petals  of  flowers  ;  ^le  bodies 
and  limbs  of  animals.  We  scarcely  ever  see  straight  lines, 
or  sharp  angles  among  them,  as  in  mineral  substances. 

Every  species  of  animal  or  vegetable  has  its  own  proper 
size,  from  which  it  varies  but  little.  But  minerals  may  be 
large  or  small ;  the  substance  called  granite,  for  example, 
may  make  a  pebble  or  a  mountain. 

6.  Inorganic  bodies  contain  either  a  single  element,  as 
carbon,  sulphur,  <S£c.,  or  several  of  the  elementary  or  simple 
substances,  which  B.Ye  fifty -two  in  number,  as  lime,  silex,  and 
magnesia  ;  while  in  organized  bodies,  we  find  at  least  three 
of  these  elements,  as  carbon,  hydrogen,  and  oxygen  in  veget- 
ables ;  and  the  same,  with  the  addition  of  azote  or  nitragen 
in  animals.  In  organic  bodies,  there  have  been  discovered 
in  all  eighteen  simple  substances,  though  they  generally  con- 
tain but  three  or  four. 

7.  But  these  two  classes  of  substances,  not  only  differ  as 
to  the  number  of  the  elements  which  enter  into  their  com- 
position, they  also  differ,  as  to  the  mode  in  which  these 
elements  are  combined.  Thus  in  minerals,  two  element- 
ary substances  unite  and  form  a  compound,  and  this  again, 
combines  either  with  another  simple  substance,  or  with  a 
compound  composed  of  two  other  simple  substances.  Thus, 
for  example,  carbonate  of  ammonia  is  composed  of  car- 
bon, oxygen,  hydrogen,  and  nitrogen,  but  combined  as 
follows  : — 

The  carbon  and  oxygen  unite  to  form  carbonic  acid  ;  the 
hydrogen  and  nitrogen,  to  form  ammorda ;  these  two  com- 
pounds thus  uniting,  form  carbonate  of  ammonia. 


ORGANIC    AND    INORGANIC    BODIES.  15 

In  animals,  we  find  the  same  simple  elements  uniting,  each 
with  all  the  others,  forming  the  peculiar  principles  of  organic 
bodies,  such  as  fibrin,  gelatine,  &c. 

8.  Organized  bodies  contain  small  particles  of  matter  of 
a  round  or  oval  shape,  both  among  their  solid  and  fluid  parts. 
These  are  supposed,  according  to  their  different  arrangement, 
to  make  up  all  the  elementary  forms  of  organized  bodies  ;  as 
when  arranged  in  lines,  they  form,  nerves,  tendons,  and 
muscles  ;  in  sheets,  the  various  membranes  and  coats  of  ves- 
sels ;  and  in  masses,  the  solid  substance  of  the  glands,  as  the 
liver,  kidneys,  and  pancreas. 

9.  There  are  but  few  changes  in  inorganic  bodies.  The 
elements  of  which  they  are  composed  remain  at  rest.  Rocks 
and  mountains  are  the  same  now,  as  they  were  five  thousand 
years  ago.  But  in  organized  bodies,  compounds  are  con- 
tinually forming  to  be  again  separated  ;  animals  feed  on 
vegetables,  and  vegetables  on  animals .; 

•'  See  dying  vegetables  life  sustain; 
See  life  dissolving,  vegetate  again  ; 
All  forms  that  perish,  other  forms  supply — 
3y  turns  we  catch  the  vital  breath  and  dieJ' 

10.  In  organized  bodies  the  parts  are  mutually  dependent 
on  each  other  for  support.  If  we  cut  off  the  limb  of  a  tree, 
it  dies,  because  it  can  receive  no  sap  ;  if  we  amputate  a 
finger,  it  mortifies,  because  the  circulation  of  the  blood  has 
ceased  ;  but  if  we  break  off  a  piece  of  marble,  it  will  remain 
unchanged  as  long  as  the  original  mass.  > 

11.  Inorganic  substances  exist  either  in  solid,  liquid,  or 
gaseous  forms.  They  are  wholly  solid,  liquid,  or  gaseous. 
But  organic  matter  always  presents  a  combination  of  solid 
and  fluid  parts.  We  find  fluids  circulating  in  regular  ves- 
sels, and  the  solids  and  fluids  mutually  dependent  on  each 
other  for  support.     In  vegetables,  we  discover  various  parts. 


16  PHYSIOLOGY. 

such  as  wood,  bark,  leaves,  roots,  and  flowers ;  and  in  ani- 
mals, muscles,  nerves,  tendons,  vessels — all  of  which  are 
organs,  or  instruments  for  the  accomplishment  of  certain 
purposes.  Inorganic  bodies  are  formed  oi  homogeneous  parts, 
or  parts  perfectly  similar. 

12.  Organic  bodies  are  composed  of  two  kinds  of  elements, 
cliemicalj  such  as  oxygen,  carbon,  and  hydrogen,  which  exist 
in  minerals  ;  and  organic,  or  proximate,  such  as  albumen,  gel- 
atine,  fibrin,  &;c.,  such  as  are  never  found  in  inorganic  mat- 
ter. It  is  because  these  organic  substances  are  produced  by 
the  peculiar  forces  of  organic  life,  and  not  by  chemical  laws, 
that  we  cannot  decompose  and  then  re-form  them,  out  of 
the  same  elements,  as  we  can  minerals.  For  example,  we 
can  dissolve  alum,  salt,  or  copperas,  and  then  by  evapora- 
tion, crystalize  them  in  the  same  shape  again.  . 

13.  The  general  'properties  of  organic  or  inorganic  bodies 
differ  in  many  particulars.  In  the  first  place  there  is  a 
constant  warfare  going  on,  between  the  chemical  and  phys- 
ical laws,  which  govern  inorganic  matter,  and  the  vital  laws 
which  maintain  animal  life.  This  conflict  commences  at 
the  first  period  of  our  existence,  and  is  kept  up  to  the  moment 
of  our  dissolution.  Life  is  enabled,  for  wise  purposes,  to 
wrest  portions  of  matter  from  the  domain  of  the  laws  of 
matter,  for  a  certain  indefinite  period ;  for  a  while,  the 
vital  powers  maintain  a  successful  contest,  but  at  last  they 
have  to  yield,  and  death  gives  over  the  body  to  the  action 
of  the  chemical  forces. 

14.  This  power  of  resisting  the  mechanical  and  chemical 
laws  of  matter,  is  shown  by  the  faculty  which  animal  bodies 
possess  of  maintaining  the  same  degree  of  temperature,  amid 
the  great  changes  from  heat  to  cold  to  which  they  are  exposed ; 
in  the  power  of  changing  to  chyle  and  blood,  the  various 
forms  of  food  on  which  they  subsist ;  and  also  in  their  power 
of  forming  from  these  the  various  tissues  and  organs  of  which 
they  are  composed,  and  all  in  opposition  to  the  general  laws 
of  matter. 


ORGANIC  AND  INORGANIC  BODIES.  17 

15.  The  growth  of  organized  bodies  proceeds  from  within, 
that  of  inorganic  matter  from  without.  If  minerals  increase 
in  size,  it  is  by  attracting  matter  to  their  external  surface, 
while  animals  and  vegetables  grow  by  a  process,  called 
nutrition  ;  that  is,  laying  hold  of  nutritious  substances  and 
converting  them  to  their  own  nature,  by  means  of  internal 
organs. 

16.  Organized  bodies  possess  the  power  of  being  affected 
with  disease  and  recovering  from  it.  They  also  have  a 
determinate  duration,  beyond  which  they  do  not  often  live. 
This  period  varies  for  each  species  of  animal  and  vegetable. 
Some  insects  live  but  a  single  day  ;  most  plants  live  but  a 
single  year ;  but  some  trees,  such  as  the  oak  and  cedar,  are 
supposed  to  live  more  than  two  thousand  years.  The  average 
duration  of  human  life  in  this  country  is  not  over  thirty  years. 

17.  But  the  great  distinction  between  a  living  being  and 
an  inorganic  body  is,  that  the  former  carries  on  a  number  of 
processes,  not  performed  by  the  latter.  A  plant,  for  example, 
absorbs  food,  converts  it  into  its  own  proper  substance, 
arranges  it  into  bark,  wood,  leaves,  and  other  organized 
structures,  grows,  arrives  at  maturity,  generates  and  main- 
tains a  certain  degree  of  heat,  decays,  and  finally  perishes. 
No  such  phenomena  are  exhibited  by  a  stone,  or  other  inor- 
ganic bodies.  These  processes,  therefore,  are  called  vital^  be- 
cause they  are  peculiai*  to  a  state  of  lifevand  afford  characters 
by  which  a  living  being  is  distinguiBhed  from  all  others. 

18.  Organized  beings  are  divided  into  two  classes,  animals 
and  vegetables,  diiffering  from  each  other  in  several  well- 
known  features. 

19.  Sensation  and  voluntary  motion  are  possessed  by  ani- 
mals, but  not  by  vegetables.  Had  animals  no  sensibility  or 
feeling,  they  could  not  know  their  wants  ;  and  if  they  knew 
them  but  had  not  the  power  of  motion,  they  would  perish  for 
want  of  food  ;  hence  the  necessity  of  these  two  faculties 
being  joined  together. 

20.  An  animal,  like  a  plant,  receives  food,  transforms  it  into 

2* 


18  PHYSIOLOGY. 

its  own  proper  substance,  and  builds  it  up  into  certain  struc- 
tures ;  it  also  generates  and  maintains  a  certain  degree  of 
temperature,  and  after  having  arrived  at  maturity  decays 
and  dies ;  but  in  addition  to  these  vital  processes  which  are 
similar  in  both,  the  animal  possesses  the  faculty  of  feeling 
and  moving  spontaneously,  or  according  to  the  dictates  of 
its  will,  a  property  peculiar  to  itself. 

21.  Vegetables  are  nourished  by  the  substances  immedi- 
ately around  them,  such  as  air,  water,  and  the  saline  proper- 
ties of  the  soil.  They  draw  their  support  from  without,  by 
absorption  at  their  surface,  or  by  means  of  roots.  But 
animals  draw  their  nutriment  from  a  great  variety  of  sources, 
and  they  are  furnished  with  an  internal  cavity  to  receive 
and  prepare  it  for  the  purposes  of  nourishment. 

22.  Vegetable  matter  is  composed  chiefly  of  i/«r€€  elements, 
viz.  carbon,  hydrogen,  and  oxygen-^  besides  these,  animal 
matter  contains  azote,  which  gives  the  peculiar  smell  that  we 
perceive  on  burning  flesh,  hair,  bones,  or  feathers.  Eighteen 
simple  substances,  however,  have  been  ^und  in  vegetables, 
in  very  small  quantities ;,  such  as  lime,  sulphur,  iodine,  silex, 
potash,  soda,  &;c. 

23.  Animals  and  vegetables  both  consist  of  solid  and  fluid 
parts ;  the  fluids,  however,  in  animals,  exist  in  much  the 
largest  proportion.  This  is  the  reason  why  decomposition 
occurs  more  rapidly  in  animals  than  in  vegetables.  Veget- 
ables, abounding  in  fluids,  decay  sooner  than  those  of  a  more 
solid  or  fibrous  texture. 

2.4.  Though  the  differences  between  animals  and  veget- 
ables, are  in  general  sufficiently  obvious  and  striking,  yet 
in  some  few  instances,  their  distinguishing  characteristics 
are  not  so  evident.  This  is  apparent  from  the  fact,  that 
some  animals  have  been  mistaken  for  vegetables,  and  some 
vegetables  for  animals.  Some  animals  we  find  to  be  as 
firmly  attached  to  the  soil,  as  most  vegetables  are,  as  is  the 
case  in  many  of  the  zoophytes,  or  lowest  order  of  animals, 
as  the  sponge,  coral,  &;c.  ;  while  on  the  other  hand,  some 


OUGANIC    AND    INORGANIC   BODIES.  19 

vegetables  float  in  the  water,  as  many  kinds  of  sea-weed, 
and  are  never  attached  to  the  soil. 


Questions. — What  is  physiology  ?  What  does  vegetable  ph3^siology 
treat  of?  What  human  ?  What  classes  does  the  kingdom  of  nature 
embrace  ?  What  other  division  ?  What  is  meant  by  organic  bodies  ? 
What  by  inorganic  ?  How  are  organic  bodies  divided  ?  How  do  or- 
ganic and  inorganic  bodies  differ  from  each  other  ?  How  do  they 
differ  as  to  form  ? — as  to  size  ? — as  to  their  number  of  elements  ? — as  to 
their  mode  of  combination  ? — as  to  the  shape  of  their  particles  ? — as  to 
the  changes  they  undergo  ? — as  to  the  mutual  dependence  of  parts  ? — as 
to  the  kinds  of  elements  ? — as  to  their  general  properties  ?  How  as  to 
their  mode  of  growth  ?  of  disease  ?  What  is  the  grand  distinction 
between  the  two  classes  of  bodies  ?  How  are  organized  beings  divid- 
ed ?  How  do  animals  and  vegetables  differ  ?  How  are  vegetables 
nourished  ?  What  is  vegetable  matter  composed  of?  Do  animals  or 
vegetables  possess  the  greatest  amount  of  fluids  ?  What  animals  have 
been  mistaken  for  vegetables  ? 


CHAPTER  II. 

DIVISION  OF  THE  AXIMAL  KINGDOJf. 

1.  CuviEE  has  divided  animals  into  four  great  groups. 
1.  The  vertebral.  2.  The  molluscous.  3.  The  articulated^ 
4.  The  radiated.  The  three  last  are  destitute  of  vertebrae, 
or  a  connected  series  of  bones  to  form  a  spinal  column. 
They  are,  therefore,  called  invertebrated,  while  the  term 
vertebrated  is  applied  to  the  former.  The  vertebral  are 
again  divided  into  four  classes,  viz.  1.  Mammalia.  2.  Birds. 
3.  Reptiles.  4.  Fishes.  These  are  also  distinguished  by 
the  terms  warm,  and  cold-blooded ;  the  warm-blooded,  in- 
cluding the  two  former,  which  possess  a  temperature  con- 
siderably above  that  in  which  they  live  ;  while  the  two 
latter,  or  the  cold-blooded  animals,  are  but  little  warmer 
than  that  of  the  medium  by  which  they  are  surrounded. 
The  mammalia  are  divided  into  nine  orders  ;  Birds  into 
six;  while  Reptiles  include  Tortoises,  Lizards,  Serpents, 
and  Frogs.  Fishes  are  divided  into  the  Cartilaginous  and 
Bojiy. 

2.  Molluscous  animals,  as  the  name  signifies,  are  those 
which  have  no  bones  corresponding  to  those  of  the  higher 
orders  of  animals.  They  include  all  those  animals  with  soft 
bodies,  which  dwell  in  calcareous  habitations,  constructed  by 
themselves  ;  many  of  them  are  accordingly  called  shell-fish, 
such  as  the  oyster,  muscle,  clam,  &;c.  This  division  also 
embraces  the  snail,  slug^  and  the  nautilus.  The  articulated 
class  includes  such  animals  as  are  furnished  with  joints, 
with  a  hard  external  crust,  or  skeleton,  to  which  are  attach- 
ed the  organs  of  motion^  It  embraces  the  annelides,  or  red- 
blooded  worms,  the  Crustacea,  (the  lobster  and  crab,)  Spiders^ 
and  Insects.  The  Radiated  class  includes  the  Zoophytes,  or 
Plant  animals,  so  called  from  their  resemblance  to  the  veget* 


PHYSIOLOGY.  21 

able  kingdom.  Most  of  these  are  of  a  soft  texture,  as  the 
Polypus,  so  well  known  from  its  being  capable  of  existing 
when  turned  inside  out,  and  of  reproducing  any  part  of  its 
body  when  destroyed  by  accident.  To  this  class  belongs 
the  Sponge,  and  the  numerous  families  of  the  Coral. 

3.  The  mammalia  are  placed  at  the  head  of  the  animal 
kingdom  ;  not  only  because  it  is  the  class  to  which  man 
himself  belongs,  but  because  it  also  enjoys  the  most  numerous 
faculties,  the  most  delicate  sensations,  the  most  varied  powers 
of  motion,  and  the  highest  degree  of  intelligence. 

4.  The  peculiar  characters  of  these  different  classes  must 
be  learned  from  works  which  treat  especially  of  Comparative 
Anatomy.  It  will  be  proper,  however,  in  this  place,  to 
point  out  some  of  the  peculiarities  which  distinguish  man, 

5.  In  structure  and  external  shape,  man  bears  considerable 
resemblance  to  some  varieties  of  the  ape  tribe,  particularly 
the  ourang  oiitang.  But  we  find  his  p)osition  to  be  upright; 
his  foot  is  large,  and  the  leg  placed  vertically  upon  it ;  while 
the  toes  are  short  and  but  slightly  flexible,  and  the  great 
toe  is  horizontal  with  the  others,  so  that  his  feet  is  well 
adapted  to  support  the  body,  but  cannot  be  used  for  seizing 
or  climbing.  Apes  have  thumhs  both  upon  their  hands  as 
well  as  feet,  so  that  they  can  seize  with  both  equally  well. 
The  head  of  man  is  also  very  large  and  heavy,  owing  to  the 
magnitude  of  the  brain,  and  the  smallness  of  the  cavities  of 
the  bones  ;  yet  the  means  of  supporting  it,  except  in  a  per- 
pendicular position  are  very  small,  as  the  ligament  of  the 
neck,  which  in  quadrupeds  is  very  thick,  in  him  is  almost 
Wanting. 

6.  Besides  this,  the  spinal  column  is  so  constructed,  that 
its  flexure  forwards  is  not  prevented,  so  that  should  he  at- 
tempt to  walk  on  all-fours,  his  mouth  and  eyes  would  be 
directed  towards  the  earth,  and  he  could  not  see  before  him, 
while  in  an  erect  attitude  he  preserves  the  use  of  his  hands, 
and  at  the  same  time  his  organs  of  sense  are  most  favorably 
situated  for  observation. 


22  PHYSIOLOGY. 

7.  Though  man  surpasses  all  other  animals  in  dexterity,  yei 
there  are  many  that  exceed  him  in  strength,  swiftness,  and 
the  acuteness  of  many  of  the  senses.  The  eagle  excells  him 
in  acuteness  of  vision,  the  grey  hound  in  delicacy  of  smell, 
and  a  vast  number  of  animals  in  strength,  yet  reason  makes 
lip  for  all  other  deficiences.  Though  physically  defenceless,- 
yet  the  whole  brute  creation  is  subjected  to  his  control. 

8.  It  was  formerly  supposed  that  man,  because  gifted  with 
the  highest  mental  endowments  possessed  the  largest  of  ail 
brains.  But  as  elephants  and  whales  surpass  him  in  this 
respect,  and  the  sagacious  monkey  and  dog  have  smaller 
brains  than  the  comparatively  stupid  ass,  hog,  and  ox,  the 
opinion  was  relinquished,  and  man  was  said  only  to  have 
the  largest  brain  in  proportion  ta  the  size  af  his  body»  But 
more  extensive  observation  proved  that  canary  and  other 
birds,  and  some  varieties  of  the  monkey  tribe,  have  larger 
t>rains  than  man  in  proportion  to  the  body,  and  several 
mammalia  to  equal  him  in  this  particular  ;  and  as  rats  and 
mice  too,  surpass  the  dog,  horse,  and  elephant  in  the  com- 
parative bulk  of  their  brains  ;  this  opinion  gave  way  to  the 
one  now  generally  adopted  by  physiologists,  viz.  that  man 
possesses  the  largest  brain  in  comparison  with-  the  nerves 
/^rising  from  it. 

9.  In  consequence  of  the  great  size  of  his  brain,  man  has 
a  larger  facial  angle,  which  is  the  space  included  by  lines 
drawn  from  the  centre  of  the  ear  to  the  root  of  the  nose,  and 
from  thence  to  the  forehead.  In  the  best  formed  human 
•heads,  this  angle  is  equal  to  80  or  90  degrees.  In  man  also, 
the  chin  is  more  prominent,  and  the  lower  front  teeth  more 
perpendicular  ;  his  teeth  also  are  of  the  same  length,  which 
is  not  the  case  in  the  inferior  animals.  Man  only  can  adapt 
himself  to  the  great  varieties  of  climate,  and  of  food,  which 
exist  on  the  surface  of  the  earth. 

10.  Lastly,  man  is  possessed  of  faculties  that  enable  him 
to  trace  effects  to  their  causes,  to  distinguish  between  virtue 
,and  vice,  to  reflect  upon  events  that  have  passQd,  to  anti- 


stuucture  of  the  human  body.      23 

cipate  the  issues  of  the  future  ;  and,  above  all,  to  raise  his 
mind  to  the  Supreme  Intelligence,  the  cause  of  causes,  to 
whom  all  nature  owes  her  existence,  and  to  whom,  with 
more  or  less  clearness  of  conviction,  he  feels  conscious  of 
responsibility. 


Questions. — How  is  the  animal  kingdom  divided  ?  "What  is  meant 
by  vertehrated,  and  what  by  invertebrate d  animals  ?  How  are  the 
Tcrtebral  divided  ?  What  is  understood  by  a  warm-blooded  animal  ? 
What  by  a  cold-blooded  ?  Into  how  many  orders  are  the  mammalia 
divided  ?  Birds  ?  Reptiles  ?  What  are  molluscous  animals  ?  What 
does  the  articulated  class  include  ?  What  the  radiated  ?  What  class 
is  placed  at  the  head  of  the  animal  kingdom?  — and  why  ?  What 
species  of  animals  does  man  most  resemble  ?  How  does  he  differ  from 
the  ape  tribe  ?  Is  man  excelled  in  any  respect  by  the  inferior  animals  ? 
Mention  some  of  the  peculiarities  of  man. 


CHAPTER  III. 

STRUCTUEE    OF   THE   HUMAN   BODY. 

1.  The  human  body  is  composed  of  solids  and  fluids. 
These  terms,  however,  are  merely  relative.  There  is  no 
fluid  which  does  not  contain  some  solid  matter  in  solution  ; 
and  no  solid  however  dense,  which  does  not  contain  some 
fluid.  The  nature  of  both  fluids  and  solids  is  essentially  the 
same,  for  we  see  one  readily  passing  into  the  other  ;  indeed 
no  fluid  long  remains  a  fluid,  and  no  solid  a  solid  ;  but  the 
fluid  is  constantly  passing  into  the  solid,  and  the  solid  into 
the  fluid. 

2.  The  relative  proportion  of  the  fluids  in  the  human 
body  much  exceeds  that  of  the  solids,  the  excess  being  about 
8  to  1.  But  the  excess  varies  according  to  the  age.  The 
younger  the  age,  the  greater  the  preponderance  of  the  fluids. 
As  age  increases,  the  fluids  gradually  diminish,  till  in  old 
age,  they  become  so  much  lessened,  that  the  body  assumes 
a  dry,  wrinkled,  shriveled  and  stiff"  appearance.  In  this 
manner  we  explain  the  softness  and  roundness  of  the  body 
in  infancy  and  youth,  and  its  hard,  unequal  and  angular 
surface  in  advanced  life. 

3.  The  fluids,  then,  are  very  important,  as  they  furnish 
not  only  the  material  out  of  which  every  part  of  the  body  is 
formed,  but  ■  they  also  furnish  the  medium  by  which  the 
noxious  and  useless  matter  is  carried  out  of  the  system. 
Every  part  of  the  body  is  a  laboratory  in  which  complicated 
and  transforming  changes  are  constantly  going  on  ;  the 
fluids  ^.re  the  materials  on  which  these  changes  are  wrought, 
and  the  vital  forces  are  the  agents  by  which  they  are  effect- 
ed.    The  fluids  either  contribute  to  form  the  blood,  or  they 


STRUCTURE    OF   THE    HUMAN   BODY. 

Constitute  the  blood,  or  having  performed  some  special  office, 
as  moistening  the  various  surfaces,  are  returned  to  the  blood  ; 
hence  according  to  their  nature,  they  are  called  aqueous, 
albuminous,  mucous,  serous,  &;c. 

4.  The  solids  are  composed  of  the  same  chemical  prin- 
ciples as  the  fluids,  and  by  analysis  are  reduced  to  the  same 
ultimate  elements.  In  the  formation  of  solids,  the  particles 
of  matter  are  supposed  to  be  arranged  in  one  of  two  modes, 
viz.,  either  in  the  form  of  minute  threads  or  Jibres,  or  of  thin 
plates  or  laminae ;  hence  every  solid  of  the  body  is  said  to 
he  fibrous,  or  laminated.  These  fibres,  or  laminae  are  vari- 
ously interwoven,  and  interlaced,  so  as  to  form  a  net- work ; 
and  the  spaces  included  between  them  are  called  areolae,  or 
cells.  According  to  some  microscopical  observers,  the  ulti- 
mate animal  solid  is  a  minute  sphere  or  globule  of  matter, 
not  exceeding  an  eighth  thousandth  part  of  an  inch  in  diam- 
eter. 

5.  The  fibrous  or  laminated  matter  is  often  so  arranged 
as  to  form  a  structure,  possessing  distinct  and  peculiar 
properties  ;  and  each  of  these  modifications  is  considered  a 
separate  form  of  organized  matter,  and  is  called  a  primary 
tissue.  These  tissues  have  been  variously  classified  by  dif- 
ferent anatomists  and  physiologists,  some  making  them  to 
consist  of  five,  viz.,  the  membranous,  the  cartilaginous,  the 
osseous,  the  muscular,  and  the  nervous;  while  others  make 
but  three,  the  cellular,  the  muscular,  and  the  nervous.  An- 
other arrangement  is  into  filaments,  fibres,  tissues,  organs, 
apparatuses,  and  systems. 

6.  A  filament  is  made  up  of  a  series  of  minute  or  primi- 
tive molecules,  arranged  in  a  row.  A  fibre  is  composed  of 
several  of  these  filaments  united  together,  as  the  muscular 
and  nervous  fibres.  A  tissue  is  supposed  to  be  composed  of 
fibi*es  disposed  in  planes,  forming  in  this  manner  an  expan- 
sion, or  when  crossing  each  other,  forming  spongy  solids, 
with  cells  interspersed  throughout.     In  this  way  are  the 

cellular,    serous,  and  mucous   membranes   formed.     When 

3 


26  PHYSIOLOGY. 

these  tissues  are  so  arranged  as  to  form  a  piece  of  animal 
mechanism,  designed  for  the  performance  of  a  certain  office^ 
they  form  what  is  called  an  organ,  as  the  lungs,  brain,  liver, 
&c.  The  action  of  this  organ  is  called  its  function.  The 
liver,  for  example,  is  an  organ  ;  the  conversion  of  the  blood 
which  passes  through  ,it  into  bile,  is  its  function.  When 
several  organs  are  associated  together  for  the  accomplish- 
ment of  a  common  object,  such  an  assemblage  is  called  an 
apparatus.  The  apparatus  of  digestion  consists  of  the  mouth, 
teeth,  esophagus,  stomach,  intestinal  canal,  liver,  pancreas, 
lacteals,  &;c.,  as  all  these  concur  in  the  process  of  digestion. 
By  system,  is  understood  an  assemblage  of  organs,  possessing 
a  similar  structure,  as  the  nervous  system,  the  muscular 
system,  &;c. 

7.  Membrane  may  be  considered  as  the  first  or  primary 
tissue.  It  is  the  simplest  form  of  organized  substance,  and 
is  extensively  employed  in  the  composition  of  the  body.  In- 
deed, it  is  the  principal  material  used  in  forming  coveringjr 
containing,  protecting,  and  fixing  every  other  component 
part  of  it.  It  is  this  which  contains  in  its  cells  the  earthy 
matter  which  goes  to  form  the  bones  ;  the  canals  in  which 
are  deposited  the  substance  which  composes  the  muscular 
and  nervous  tissues ;  which  forms  a  covering  for  the  whole 
body  ;  which  lines  all  its  internal  surfaces  ;  surrounds  alF 
its  internal  organs  ;  which  makes  up  the  solid  portion  of 
every  part  of  the  system ;  forming  the  tubes  and  vessels, 
such  as  the  arteries  and  veins  ;  it  connects  all  parts  of  the 
body  together,  and  fixes  them  in  their  several  situations  ;  ia 
short,  it  is  the  substratum,  or  mould,  in  which  all  the  other 
particles  are  deposited,  thus  giving  form  and  outline  to  the 
whole  body,  so  that  if  every  other  kind  of  animal  matter 
were  removed,  this  tissue  alone  would  preserve  the  exact 
figure  and  present  a  perfect  skeleton  of  the  whole,  and  of  every 
one  of  its  parts. 

8.  There  are  several  kinds  of  membrane  ;  the  simplest  form 
of  which,  and  that  from  which  all  the  others  are  supposed  to 


STRUCTURE    OF    THE    HUMAN    BODY.  27 

be  produced,  is  termed  the  cellular.  It  is  this  which  I  have 
already  alluded  to  as  entering  into  the  compositions  of  every 
organ,  and  forming  the  basis  of  the  solid  structure  of  the 
body.  Into  its  cells  all  other  kinds  of  animal  matter  are  de- 
posited as  phosphate  of  lime  and  gelatine,  which  form  the  bones. 
It  forms  sheaths  for  the  muscles  and  nerves  ;  composes  a  great- 
er part  of  the  ligaments,  tendons,  and  cartilages,  and  even  the 
hair  and  nails,  thus  constituting  not  only  the  basis  of  all  the 
solids,  but  serving  as  a  bond  of  union  by  which  the  organs 
are  connected  together.  By  its  softness  and  elasticity,  and 
the  oily  fluid  by  which  its  cells  are  filled,  it  also  promotes 
the  mobility  of  the  parts  on  one  another.  It  possesses  the 
property  o{  contractility,  and  is  composed  chiefly  o^  gelatine* 
9.  One  remarkable  circumstance  connected  with  this  tis- 
sue is,  that  as  it  exists  throughout  the  body,  it  forms  a  con- 
nected whole,  or  an  immense  net-work,  every  where  accessi- 
ble to  air.  This  is  shown  by  forcing  air  into  its  cells,  in 
any  part  of  the  body  ;  which  is  found  gradually  to  penetrate 
and  pervade  every  part  till  the  whole  body  is  inflated. 
Butchers  often  avail  themselves  of  a  knowledge  of  this  fact, 
by  blowing  their  meat,  or  in  other  words,  inflating  animals 
by  making  a  puncture  in  some  part  where  the  cellular  tissue 
is  loose,  and  from  this  one  aperture  forcing  the  air  to  the 
most  distant  parts  of  the  body,  in  order  to  give  the  meat  a 
fat  appearance.  If  we  raise  up  a  portion  of  cellular  mem- 
brane, in  the  form  of  a  thin  slice,  it  appears  as  a  semi-trans- 
parent and  colourless  substance,  composed  of  minute  threads 
which  are  seen  to  cross  each  other  in  every  possible  direction, 
leaving  spaces  between  them,  and  thus  forming  a  mesh, 
similar  to  the  spider's  web.  As  to  the  precise  form  of  these 
cells  or  cavities  we  have  no  accurate  knowledge.  They  are 
generally  supposed  to  be  narrow  spans  with  acute  angles,  the 
sides  of  which  are  flattened,  and  when  not  forcibly  expanded, 
we  may  suppose  to  be  in  contact.  Some  physiologists  in- 
deed deny  that  any  cavities  at  all  exist,  but  the  weight  of 
evidence  is  altogether  in  favour  of  their  existence. 


28 


PHYSIOLOGY. 


flg^^l^AiM^-JlifJ^^i^^^^'^'^f^^W^^ 


.imj..iii&>mm^m^ 


A  single  film  of  the  cellular  tissue  lifted  up,  and  slightly  distended. 

10.  In  health,  the  spaces  between  these  lines  are  filled  with 
a  thin  exhalation  of  a  watery  nature,  which  serves  to  keep 
the  tissue  always  soft  and  moist.  This  is  composed  of  the 
thinner  part  of  the  blood,  which  is  poured  out  by  a  process 
called  secretion,  but  is  speedily  taken  up  again  by  absorption. 
These  two  operations  exactly  balance  each  other  in  health, 
but  when  from  any  cause  the  equilibrium  is  disturbed,  the 
fluid  accumulates,  constituting  the  disease  called  dropsy. 
This  is  often  relieved  by  the  operation  of  tapping,  or  draw* 
ing  off  the  water.  Cellular  membrane  is  dense  or  loose, 
coarse  or  fine,  according  to  its  situation  and  ofiice.  Wha|8 
it  is  subject  to  pressure,  as  in  the  palm  of  the  hand  and  soio^ 
of  the  foot,  it  is  dense  and  firm  ;  around  the  internal  organa 
it  is  more  loose  and  delicate.  Although  cellular  tissue  en- 
ters into  the  composition  of  all  the  organs,  it  never  loses  its 
own  character,  nor  participates  in  the  functions  of  the  organ, 
of  which  it  forms  a  part.  Though  present  in  the  nerves  it 
does  not  share  in  their  sensibility,  and  though  it  accompa- 
nies every  muscle  and  every  muscular  fibre,  it  nowhere  par- 
takes of  the  irritability  which  belongs  to  these  organs.  The 
microscope  shows  that  the  minute  particles  of  this  tissue  are 
of  a  globular  figure,  arranged  like  strings  of  pearls,  as  repre- 
sented in  the  following  cut. 


STRUCTURE    OF    THE    HUMAN   BODY. 


29 


A  portion  of  cellular  tissue,  very  highly  magnified,  showing  the 
strings  of  globules  of  which  its  ultimate  fibres  are  supposed  to  consist. 

1 1 .  The  principal  varieties  of  membrane,  which  are  formed 
by  the  cellular  tissue,  are  the  adipose,  the  serous,  the  mucous, 
the  dermoid,  the  fibrous,  the  cartilaginous,  and  the  osseous. 
The  adipose  is  that  tissue  which  contains  the  fat  which  is  so 
disposed  as  to  form  distinct  bags  in  which  the  fat  is  con- 
tained. Now  it  should  be  recollected,  that  while  the  cells  of 
the  cellular  tissue  are  continuous  over  the  whole  body,  each 
adipose  vesicle  is  a  distinct  bag,  having  no  communication 
whatever  with  any  other.  While  also,  the  cellular  tissue  is 
Amiversally  disposed,  the  adipose  is  placed  only  in  particular 


2  2 

1,  A  portion  of  adipose  tissue :  2.  minute  bags  containing  the  fat 
3.  a  cluster  of  the  bags,  separated  and  suspended. 

3* 


30  PHYSIOLOGY. 

parts  of  the  body,  principally  beneath  the  skin  and  the  ab» 
dominal  muscles,  and  around  the  heart,  kidneys,  &;c.  while 
none  is  ever  found  in  the  cranium,  the  brain,  the  eye,  the 
ear,  the  nose,  and  several  other  organs. 

12.  The  Serous  Membranes. — These  line  all  the  closed 
cavities,  or  sacs  of  the  body,  and  are  reflected  over  the  or- 
gans contained  in  them.  Thus  the  cavities  of  the  brain  and 
chest,  the  abdomen  and  joints,  are  lined  by  serous  membrane. 
By  its  external  surface,  it  is  united  to  the  walls  of  the  cavity, 
or  the  substance  of  the  organ  it  invests  ;  by  its  internal  sur- 
face it  is  free  and  unattached  ;  whence  this  surface  is  in  con- 
tact only  with  itself,  forming  a  close  cavity,  having  no  com- 
munication with  the  external  air. 

13.  If  it  were  possible  therefore  to  dissect  serous  membranes 
from  off  the  parts  which  they  invest,  they  would  have  the 
form  of  a  sac,  without  an  opening,  the  organ  invested  by  one 
of  these  folds  being  altogether  external  to  the  cavity  of  that 
sac ;  just  as  happens  when  a  double  night-cap  is  worn,  of 
which  the  part  immediately  covering  the  head  is  analagous 
to  that  portion  of  the  serous  membrane  which  adheres  to  and 
invests  the  organ,  whilst  the  external  portion  of  the  cap 
represents  the  lining  of  the  cavity  in  which  that  organ  is 
said  to  be  contained.  Hence  it  will  readily  be  understood 
that  the  serous  membranes  never  open,  or  allow  of  any  per- 
foration for  the  passage  of  blood-vessels,  nerves,  or  ducts,  to 
or  from  the  enclosed  organs  ;  but  that  they  are  always  re- 
flected over  them,  forming  a  sheath  around  them,  and  accom- 
panying them  in  their  course.  It  also  follows  as  a  necessary 
consequence,  that  their  free  surfaces  completely  isolate  the 
parts  between  which  they  intervene. 

14.  The  serous  membranes  are  of  a  whitish,  shining  col- 
our, and  smooth  on  their  free  or  inner  surface.  They  are 
kept  constantly  moist  by  a  fluid  which  is  exhaled  in  a 
gaseous  state  from  the  serum  of  the  blood,  whence  they 
derive  their  name.  They  are  also  elastic  and  extensible, 
and  are  said  to  be  destitute   of  blood-vessels  and   nerves; 


STRUCTURE    OF    THE    HUMAN    BODY. 


m 


being  composed  of  condensed  cellular  membrane.  Accord- 
ing to  Rudolphi,  serous  membranes  line  not  only  the  closed 
cavities  of  the  body,  but  the  interior  of  the  vessels  also, 
and  the  canals  which  open  outwardly,  as  the  alimentary 
canal  and  the  air  passages,  forming  a  cuticle  over  the  mu- 
cous membranes,  which  line  these  passages.  The  uses  of 
the  serous  membranes  are  to  separate  different  organs,  to 
diminish  friction,  and  to  facilitate  the  motion  or  gliding  of 
these  parts  upon  one  another,  by  means  of  thin  smooth, 
moist,  and  polished  surfaces. 


15.  Mucous  Membranes. — These  membranes  are  also 
another  form  of  the  cellular  structure,  and  derive  their  name 
from  the  nature  of  the  fluid,  which  it  is  their  office  to  secrete 
by  means  of  numerous  minute  glands  imbedded  in  their  sub- 
stance. As  serous  membranes  form  a  shut  sac,  completely 
excluding  the  air,  mucous  membranes  on  the  contrary,  line 
the  various  cavities,  which  are  exposed  to  the  air,,  such  as 
the  mouth,  the  nostrils,  the  windpipe,  the  gullet,  the  stomach, 
the  intestines,  and  the  urinary  organs.  Their  internal  sur- 
face, or  that  by  which  they  are  attached  to  the  passages  they 
line,  is  smooth  and  dense,  while  their  external  surface,  or  that 
which  is  exposed  to  the  contact  of  the  air,  is  soft  and  pulpy^ 
like  the  pile  of  velvet,  or  the  rind  of  a  ripe  peach. 


32  PHYSIOLOGY. 


A  portion  of  the  stomach,  showing  its  internal  surface  or  mucous  coat. 

16.  The  mucous  coat  is  the  seat  of  some  of  the  most  im- 
portant  functions  of  the  economy  ;  in  the  lungs,  of  respira- 
tion ;  in  the  stomach,  of  digestion ;  and  in  the  mouth  and 
nose,  of  taste  and  smell,  &;c.,  and  forms,  with  scarcely  an 
exception,  a  continuous  whole.  That  portion  which  lines 
the  eyes  and  eyeJids,  is  connected  with  that  which  lines  the 
nostrils,  by  means  of  the  nasal  canal ;  while  that  which  lines 
the  mouth,  meets  in  the  throat  with  that  which  comes 
down  from  the  nose.  In  the  fauces  it  divides,  and  while  one 
portion  goes  down  the  windpipe  into  the  lungs,  the  other 
passes  down  the  esophagus  into  the  stomach,  forming  a  lining 
for  the  whole  tract  of  the  intestinal  canal. 

17.  Mucous  membranes  are  of  a  loose,  spongy  texture,  of 
a  reddish  colour,  and  are  largely  supplied  with  blood-vessels 
and  nerves.  They  are  also  numerously  supplied  with  small 
glandular  bodies  called  mucous  glands  or  folicles.  The 
chief  use  of  these  membranes  is,  to  sheath  and  protect  the 
inner  surfaces  of  the  body,  as  the  skin  does  the  outer,  and  by 
means  of  the  mucus,  with  which  they  are  always  covered  in 
a  state  of  health,  to  guard  them  against  the  contact  of  irri- 
tating substancesi.^ 


STRUCTURE    OF    THE    HUMAN    BODY.  33 

18.  We  find  a  remarkable  sympathy  existing  between  all 
the  mucous  membranes  ;  accordingly  their  diseases,  particu- 
larly the  catarrhal  affections,  to  which  they  are  often  sub- 
ject, are  very  apt  to  spread  in  them.  By  reason  of  this  sym- 
pathy, the  state  of  one  part  of  these  membranes  may  be  as- 
certained by  examining  another  part ;  the  state  of  the  tongue 
for  example,  indicates  the  condition  of  that  of  the  stomach 
and  intestinal  canal.  There  is  also  an  extraordinary  sym- 
pathy between  the  mucous  membranes  and  the  respiratory 
organs. 

19.  Dermoid  Memhrane. — This  membrane,  called  also 
cutis  or  skin,  is  not  only  directly  continuous  with  the  mu- 
cous membranes  that  line  the  internal  passages,  but  is  also 
analagous  in  its  structure.  We  see  them  passing  into  each 
other  at  the  orifices  of  the  internal  canals,  as  in  the  lips,  nos- 
trils,  eye-lids,  external  ear,  &c.  We  find  it  varying  in  thick- 
ness according  to  its  situation  ;  in  the  face  and  body  being 
thin  and  delicate,  and  on  the  palms  of  the  hands  and  soles  of 
the  feet,  considerably  firmer  and  thicker.  The  skin  is 
abundantly  supplied  with  blood-vessels  and  nerves ;  so  nume- 
rous indeed,  that  the  finest  needle  cannot  enter  the  skin 
without  piercing  many  of  both,  which  is  proved  by  the  bleed- 
ing, as  well  as  the  pain  which  follow. 

20.  The  skin,  in  man,  is  made  up  of  four  parts,  or  layers^ 
the  cuticle,  rete-mucosum,  corpus  papillare,  and  corium.  It 
is  covered  externally  by  the  cuticle  or  epidermis,  which  is 
destitute  of  nerves  and  blood-vessels,  insensible,  and  probably 
inorganic.  It  is  the  cuticle  which  is  raised  by  the  applica- 
tion of  a  blister,  or  by  a  burn  or  seald.  It  is  supposed  to  be 
a  secretion  from  the  true  skin  which  concretes  on  the  surface 
becomes  dry,  and  thus  offers  protection  to  the  parts  beneath, 
and  also  serves  to  prevent  excessive  absorption  or  the  escape 
of  the  fluids  by  evaporation.  It  is  pierced  by  little  pores,  for 
the  passage  of  hairs,  sweat,  and  the  fluids,  taken  up  by  ab- 
Borption,  although  Humboldt  asserts  that  he  could  not  discover 
tlxem  with  a  miscroscope  which  magnified  312,000  times. 


34  PHYSIOLOGY. 

21.  The  next  layer  of  the  skin  is  the  rete  mucosum,  or 
mucous  web.  It  has  been  supposed  to  consist  chiefly  of 
mucus,  as  it  is  of  a  soft  pulpy  texture.  It  is  the  seat  of  the 
coloring  matter  in  the  different  races.  In  the  European,  it 
is  white,  in  the  African  black,  and  in  the  Mulatto  and  Malay, 
copper-coloured.  In  the  Ethiopian  race,  it  is  much  thicker 
than  in  the  light-coloured  varieties  of  the  human  species,  and 
may  easily  be  separated  both  from  the  cutis  and  cuticle,  and 
made  to  appear  as  a  distinct  membrane. 

22.  The  dark  color  of  the  skin  in  the  inhabitants  of  the 
torrid  zone,  is  ascribed  by  most  physiologists,  to  the  influence 
of  the  sun  upon  the  surface  of  the  body  ;  but  the  tinge  pro- 
duced on  the  skin  by  exposure  to  a  bright  light,  appears 
to  have  no  connection  with  the  permanent  colour  of  the 
negro.  Dr.  Bostock  states,  that  the  blackest  complexions 
are  not  found  in  the  hottest  regions,  and  that  there  are 
some  tribes  nearly  under  the  equator,  whose  skin  is 
whiter  than  that  of  many  Europeans.  Besides,  the  tinge 
produced  by  the  sun  is  not  transmitted  from  parents  to 
their  offspring,  whereas  the  children  of  negroes  are  equally 
black  in  whatever  climate  they  are  born,  and  their  com. 
plexion  is  not  altered  by  any  number  of  generations.  When 
a  person  is  tanned,  as  it  is  called,  by  the  influence  of  the 
sun,  it  is  the  cuticle  only  which  is  affected  ;  if  this  be 
removed  by  a  blister,  in  a  few  days  new  cuticle  will  be 
formed,  and  the  skin  in  that  place  will  appear  as  white  as  it 
ever  did. 

23.  Albinos. — In  the  Caucasian  race,  from  which  Europe- 
ans and  Americans  have  descended,  there  is  usually  a  mix- 
ture of  red  or  brown,  with  white  in  the  complexion  ;  but 
where  the  skin  is  of  a  unifoi*m,  clear,  pearly  whiteness,  the 
individuals  are  called  Albinos,  from  albus,  white.  In  these 
persons,  the  hair  is  generally  white,  corresponding  with  the 
colour  of  the  skin,  while  the  eye  is  without  that  substance 
which  gives  the  various  coloui's  to  the  iris.    The  iris,  in  such 


STRUCTURE    OE    THE    HUMAN    BODY.  35 

cases,  is  generally  of  a  bright  rose-colour,  and  the  eyes  are 
so  sensible  to  light,  that  they  cannot  be  kept  open  in  the 
sun-shine,  although  in  the  shade,  or  dusk  of  the  evening,  the 
vision  is  perfect.  It  is  now  w^ell  ascertained  that  the  red- 
ness of  the  eye  and  the  whiteness  of  the  skin  in  albinos 
depends  on  the  same  physical  defect  in  their  organization, 
and  that  it  is  owing  to  the  absence  of  the  colouring  mat- 
ter in  the  rete  mucasum.  In  the  eye,  this  matter,  spread 
over  the  retina,  is  called  Pigmentum  nigrum,  or  the  black 
paint. 

24.  What  is  called  the  Corpus  papillare,  is  merely  a  col- 
lection of  small  papillae,  formed  by  the  extremities  of  nerves 
and  blood-vessels,  and  lying  immediately  under  the  mucous 
web,  &;c.  It  is  in  this  layer  that  the  sense  of  touch  resides  ; 
the  papillae  can  easily  be  seen  when  the  cuticle  has  been 
removed  by  a  blister. 

25.  The  Cutis  vera,  or  true  skin,  is  the  innermost  of  the 
four  layers  above  mentioned.  It  is  a  firm  stratum  of  dense 
fibres  intersecting  each  other  in  every  direction,  and  having 
holes  for  the  passage  of  vessels  and  nerves. 

26.  The  true  skin  is  composed  chiefly  of  gelatine,  and  hence 
is  used  for  the  manufacture  of  glue.  Gelatine  combined 
with  tannin,  which  is  a  proximate  vegetable  principle  ob- 
tained from  oak  and  other  barks,  forms  a  compound  that  is 
insoluble  in  water ;    and  it  is  to  this   circumstance   that 

Jeather  owes  the  properties  it  possesses.  Leather,  then,  may 
be  considered  as  the  product  of  the  union  of  tannin  and 
gelatine. 

27.  Though  the  skin  consists  of  four  distinct  strata,  yet 
it  is  only  from  one-sixth  to  one-fourth  of  an  inch  in  diameter. 
The  true  skin  is  united  to  the  structure  below  by  cellular 
membrane,  and  this,  with  the  layers  above  described,  consti- 
tute the  common  integument.  The  following  sketch  repre- 
sents the  several  layers  entering  into  the  composition  of  the 
skin. 


36 


PHYSIOLOGY. 


6— 


1.  Cuticle, 

2.  Rete  mucosum. 

3.  Corpus  papillare. 

4.  Cutis  vera- 

5.  Cellular  membrane. 

6.  Paniculus  caraosus. 


There-  are  in  certain  parts  of  the  body,  and  especially  in 
animals,  muscular  fibres  passing  up  through  the  cellular 
membrane,  and  inserted  obliquely  into  the  cutis  vera,  as  at 
6  in  the  plate.  These  form  the  muscular  web,  or  paniculus 
carnosus.  It  is  this  which  raises  the  feathers  in  birds  and 
which  in  the  hedgehog  and  porcupine  rolls  up  the  body,  and 
erects  the  spines  ;  and  by  means  of  this,  animals  shake  off 
flies  from  their  skin. 

28.  The  skin  is  defended  from  the  action  of  moisture,  and 
is  also  kept  soft  and  pliant  by  an  oily  fluid,  which  is  separ- 
ated from  the  blood  by  numerous  sebaceous  follicles.  We 
find  these  the  most  numerous  where  there  are  folds  of  the 
skin,  or  hairs,  or  where  the  surface  is  exposed  to  friction. 
We  sometimes  see  the  oily  matter  secreted  by  these  glands 
assume  a  dark  appearance,  in  the  form  of  black  specks,  scat, 
tered  over  the  face,  which  are  called  by  many  worms,  because 
when  pressed  out  they  assume  that  aspect. 

29.  The  hair  is  usually  treated  of  by  physiologists  as  an 
appendage  to  the  skin.  The  hair  takes  its  origin  from  the 
cellular  membrane  in  the  form  of  hulbs,  each  bulb  consisting 
of  two  parts ;  an  outer,  which  is  vascular,  and  from  which 
the  hair  obtains  its  nourishment ;  an  inner,  which  is  mem- 
braneous, and  which  forms  a  sheath  or  tube  to  the  hair  during 
its  passage  through  the  skin.  The  external  covering  of 
each  hair  is  of  a  horny  structure,  while  the  central  part  is 


STRUCTURE    OF    THE    HUMAN    BODY. 


37 


soft  and  pulpy,  and  is  called  medulla,  or  pith.  The  colour 
of  the  hair  varies  in  different  individuals,  and  is  generally 
supposed  to  depend  on  the  fluids  contained  in  the  pith.  The 
hair,  it  is  said,  has  been  known  in  several  instances  to  have 
changed  from  black  to  grey  in  the  course  of  a  single  night, 
from  the  effects  of  grief,  fear,  or  some  other  great  mental 
agitation.  Vauquelin  supposes  that  as  the  colouring  matter 
of  the  hair  is  destroyed  by  acids,  this  phenomenon  is  owing 
to  the  production  of  some  acid  in  the  system.  Others  sup- 
pose that  the  effect  depends  upon  the  sudden  stagnation  of 
the  vessels  which  secrete  the  colouring  matter,  while  the 
absorbents  continue  to  act  and  remove  that  which  already 
exists.  There  are  probably  two  causes  which  act  in  chang- 
ing the  hair  to  grey  ;  the  ^rst  is  a  defective  secretion  of  a 
colouring  fluid,  and  the  second,  the  canals  which  convey  the 
fluid  into  the  hair  become  obliterated.  In  the  first  case,  the 
hair  will  remain  ;  in  the  last,  it  inevitably  dies  and  drops 
out. 


38  PHYSIOLOGY. 

30.  The  figure  on  the  last  page  represents  the  pulp  of  a 
hair  injected  ;  1,  cut  surface  of  hair  ;  2,  the  pulp  ;  3,  inject- 
ed vessel  ramifying  in  it.  The  figure  on  the  right  shows 
the  hair  in  its  fallicle,  though  the  drawing  was  made  from 
the  whisker  of  a  Walrus  ;  2,  the  cutis ;  3,  external  sheath  of 
the  fallicle  ;  4,  internal  sheath  continuous  with  the  cuticle  ; 
5,  pulp  ;  6,  shaft  of  hair ;  7,  large  nerve  going  to  it. 

31.  The  nails  are  also  an  appendage  to  the  skin.  Their 
chief  use  seems  to  be  to  support  the  pulp  of  the  finger  while 
it  is  exercising  touch.  Animals  are  provided  with  struc- 
tures analogous  in  their  physical  and  vital  properties,  such 
as  horns,  beaks,  hoofs,  nails,  spurs,  scales,  &;c.  Some  physi- 
ologists consider  the  teeth  as  belonging  to  the  same  classr 
The  various  and  peculiar  functions  of  the  skin,  so  important 
to  be  understood  in  order  to  the  preservation  of  the  health, 
will  be  fully  described  hereafter. 

Questions. — Of  what  is  the  human  body  composed  ?  What  is  said 
of  the  identity  of  solids  and  fluids  ?  What  proportion  do  the  fluids 
bear  to  the  solids  ?  How  modified  by  age  ?  What  purposes  do  the 
fluids  serve  ?  What  is  said  of  the  solids  ?  How  are  their  particles^ 
arranged  to  form  the  different  organs  ?  How  are  the  areolae  formed  ? 
Of  what  shape  is  the  ultimate  animal  solid  ?  What  is  a  primary  tissue  T 
How  many  primary  tissues  are  there  ?  What  is  a  filament  ? — a  fibre 
— a  tissue — an  organ — a  function  ?  Give  an  example  ?  What  is  an 
apparatus  ? — a  system  ? — membrane  ?  What  are  its  uses  ?  What  is 
the  simplest  form  of  membrane  ? — its  use  ?  Wliat  property  does  it 
possess  ?  What  its  chemical  composition  ?  What  remarkable  circum- 
stance connected  with  it  ?  What  is  the  seat  of  dropsy  ?  What  varie- 
ties of  membrane  are  formed  by  the  cellular  tissue  ?  Describe  the 
adipose  ?  What  are  serous  membranes  ? — where  found  ? — their  use  T 
structure  ?  What  are  mucous  membranes  ?  Describe  their  structure, 
situation,  use,  &c.  What  is  the  skin  a  continuation  of  ?  Of  how  many 
parts  is  it  composed  ?  What  is  the  external  layer  called  ? — what  is  its 
use  ?  What  is  the  layer  next  to  the  cuticle  called  ?  Of  what  is  it  the 
seat  ? — the  next  layer  ? — its  use  ?  Describe  the  cutis  vera  ?  What  is- 
it  used  for  ?  How  thick  is  the  skin  in  man  ?  By  what  contrivance  is 
the  skin  susceptible  of  motion  ?  How  is  the  skin  kept  soft  and  pliant  T 
What  is  said  of  the  hair  ? — what  is  its  structure  ? — what  is  its  colour 
owing  to  ?    What  causes  it  to  turn  grey  ?    What  is  said  of  the  nails  ? 


CHAPTER  IV. 

STRUCTURE    OF    THE    HUMAN    BODY    CONTINUED. 

1.  Another  form  of  cellular  structure  is  called ^6roM^, 
from  the  arrangement  of  its  component  parts,  which  consist 
of  longitudinal  fibres,  plainly  visible  to  the  naked  eye,  placed 
parallel  to  each  other  and  closely  united.  These  fibres  are 
sometimes  so  combined  as  to  form  a  thin,  smooth,  dense,  and 
strong  membrane,  like  that  which  covers  the  external  surface 
of  bones,  termed  periosteum,  or  the  internal  surface  of  the 
skull,  (dura  mater.)  At  other  times  it  forms  a  firm  sheath, 
■which  dips  down  between  the  muscles,  separating  them  from 
each  other,  or  it  may  be  spread  over  them,  binding  them 
firmly  down  in  their  places. 

2.  In  the  loins  and  along  the  back  bone  there  is  a  strong 
binder  of  this  kind,  which  greatly  facilitates  the  motions  of 
the  body  and  powerfully  contributes  to  the  action  of  the 
muscles.  Where  this  is  weak,  a  belt  round  the  waist  is  of 
considerable  service,  but  in  a  well-formed  person  it  is  a 
clumsy  substitute  of  art  for  nature,  and  ultimately  tends  to 
weaken  the  back,  for  exercise  strengthens  and  invigorates  all 
parts  of  the  frame,  while  artificial  substitutes  invariably 
weaken  the  parts  they  are  supposed  to  strengthen. 

3.  It  also  constitutes  the  strong,  tough,  and  flexible  band, 
used  for  tying  parts  firmly  together,  termed  ligaments,  such 
as  are  found  about  the  joints,  connecting  the  bones  ;  and  it 
also  forms  those  white  cords  in  which  muscles  terminate, 
called  tendons,  which  serve  to  attach  the  muscles  to  the 
bones,  thus  acting  as  mechanical  instruments  of  motion. 
This  tissue  forms  a  firm  covering  or  envelope  to  the  bones, 
muscles,  tendons,  cartilages,  the  eye,  kidneys,  spleen,  and 
most  of  the  organs  of  the  body. 


40  PHYSIOLOGT. 

4.  Every  joint  is  enclosed  by  a  firm  fibrous  bag,  called 
the  capsular  ligament,  the  internal  surface  of  which  secretes  a 
fluid,  termed  synovia,  which  lubricates  the  joints,  and  serves 
the  same  purpose  that  oil  does  in  a  piece  of  machinery.  At 
the  wrist  and  ankle,  and  along  the  fingers  and  toes,  the  liga- 
ments form  strong  bandages  to  bind  down  the  muscles  and 
tendons,  and  enables  them  to  act  with  greater  precision  and 
steadiness ;  otherwise  when  the  muscle  contracted,  the  ten- 
dons would  start  out  like  the  string  of  a  bow,  and  thus  not 
only  destroy  the  symmetry  of  the  parts,  but  entirely  prevent 
motion.  When  sprained  by  over  exertion  or  accident,  an 
artificial  bandage  becomes  necessary  ;  we  then  find  how  su- 
perior the  natural  ligaments  are  to  any  artificial  bandage  that 
can  be  contrived. 

5.  Tendon  or  Sinew. — This  well-known  structure  is 
plainly  perceptible  at  the  wrist,  on  the  back  of  the  hand,  at 
the  heel,  &;c.  They  have  a  white,  pearly  lustre,  possess 
great  strength,  but  little  elasticity.  They  are  composed 
of  bundles  of  parallel  threads,  bound  together  by  trans- 
verse threads,  and  they  vary  both  in  figure  and  extent ;  some 
being  cylindrical  and  tapering  to  the  point  of  insertion, 
and  in  others  forming  broad  expansions.  So  insensible  are 
tendons,  that  when  ruptured,  as  the  tendon  of  Achilles  at  the 
heel,  not  the  slightest  pain  is  felt,  but  the  person  feels  that  he 
has  received  a  smart  blow,  or  that  a  part  of  the  floor  has  give:i 
w^ay  under  him. 

6.  Where  force  is  to  be  exerted  upon  some  distinct  point,  it 
is  transmitted  along  a  tendon,  as  forces  in  machinery  are  by 
ropes.  When  a  tendon  passes  over  a  joint,  a  bone  is  formed 
sometimes  where  it  crosses,  as  the  knee-pan  in  front  of  the 
knee  joint ;  which  is  a  bone  placed  directly  in  the  centre  of 
the  tendon,  and  serves,  to  throw  the  force  farther  from  the 
centre  of  motion,  thereby  increasing  the  lever,  and  conse- 
quently the  effect.  Similar  bones  are  often  found  in  the 
tendons  of  the  ^qqU 


STRUCTURE    OF    THE    HUMAN    BODY 


41 


1.  Another  primary  tissue,  or  modification  of  cellular 
structure,  is  termed  the  cartilaginous.  This  seems  to  be  a 
substance  intermediate  between  membrane  and  bone.  It  is 
firm,  smooth,  highly  elastic,  of  a  pearly  white  colour,  and  ex- 
cept bone,  the  hardest  part  of  the  animal  frame.  It  is  des- 
titute of  red  vessels,  and  neither  nerves  nor  lymphatics  have 
been  discerned  in  it ;  though  as  it  becomes  highly  sensible, 
like  the  fibrous  tissue,  by  disease,  it  no  doubt  is  supplied  with 
nerves.  It  is  placed  at  the  ends  of  the  bones,  particularly 
about  the  joints,  where  by  its  smooth  surface,  it  facilitates 
amotion,  and  by  its  yielding  nature,  prevents  the  shock  or  jar 
which  would  be  produced  were  the  same  kind  and  degree  of 
motion  effected  by  a  rigid  and  inflexible  substance.  Where 
strength  and  flexibility  are  required  to  be  united,  we  there 
find  cartilage,  as  in  the  spinal  column,  between  the  ribs  and 
breast  bone,  in  the  laiynx,  the  ear,  nose,  &;c. 


Portions  of  cartilage  seen  in  section. 


8,  By  immersing  cartilage  in  nitric  acid  and  then  in  wa- 
ter for  some  little  time,  we  find  its  intimate  structure  so  un- 
folded, that  we  can  perceive  it  to  be  composed  of  an  infinite 
number  of  minute  fibres,  arranged  perpendicularly  like  the  pile 
of  velvet.  Thus  we  see  that  in  the  construction  of  the  joints, 
millions  and  millions  of  springs  of  the  most  curious  and  ex- 
cellent contrivance  stand  perpendicular  to  the  direction  of 
the  force  applied,  bend  to  pressure,  and  on  its  removal,  regaio 

3* 


42  PHYSIOLOGY. 

their  foi'm  by  their  elasticity.  When  we  stand  in  the  erect 
posture,  the  number  of  minute  but  efficient  springs  on  which 
the  weight  of  the  body  rests,  in  the  several  joints  of  the  back, 
in  the  hip,  knee,  and  ankle  joints,  infinitely  surpasses  the 
powers  of  the  human  mind  to  calculate  or  even  to  imagine. 

9.  There  is  a  peculiar  tissue,  allied  to  ligament  in  its  tex- 
ture, distinguished  by  a  high  degree  of  elasticity,  fibrous 
structure,  and  tawny  colour,  and  is  hence  often  called  elastic 
tissue.  This  structure  is  very  conspicuous  in  the  neck  of 
those  animals,  which  have  to  support  a  heavy  load  horizon- 
tally, at  the  the  extremity  of  a  long  neck,  as  in  the  elephant, 
the  deer,  and  our  domestic  cattle.  Had  their  heads  been 
supported  merely  by  muscular  action,  as  that  is  liable  to  fa- 
tigue and  requires,  intervals  of  rest,  as  well  as  the  exercise  of 
volition,  the  postures  could  not  have  been  sustained  for  any 
length  of  time  without  pain  and  exhaustion.  This  tissue, 
which  is  liable  to  none  of  these  objections,  is  accordingly 
substituted  for  muscular  power,  in  fixing  the  forms,  preserv- 
ing the  attitudes,  and  contributing  to  motion.  The  strong 
fibrous  band,  stretching  along  the  back  part  of  the  neck  to 
the  head  of  these  animals,  enables  them  with  perfect  ease  to 
support  the  head.  It  is  the  elasticity  of  this  membrane 
which  causes  the  head  of  these  animals  to  be  bent  back  after 
death,  the  action  of  the  muscles  having  ceased.  It  also  re- 
tracts  and  retains  the  sharp  claws  of  the  cat  tribe  within 
their  sheath  when  not  in  use.  A  ligament  of  this  tissue  also 
retains  the  wings  of  birds  in  a  bent  position  when  they  are 
in  a  state  of  rest. 

10. — The  osseous  fabric. — The  osseous  or  bony  tissue  is 
another  form  of  cellular  matter.  The  bones  constitute  the 
hardest  and  the  most  solid  parts  of  the  whole  system,  and  are 
the  principal  parts  that  give  it  form  and  stability,  forming  as 
it  were,  the  frame  work  of  the  animal  machine.  The  num. 
ber  of  bones  in  the  human  adult,  including  the  teeth,  is  245. 
When  we  examine  the  broken  surface  of  a  bone,  with  a  mi- 
croscope,  we  find  it  abundantly  supplied  with  minute  blood- 


STRUCTURE    OF    THE    HUMAN    BODY. 


4S 


vessels,  without  any  appearance  of  fibres  or  plates.  The 
different  densities  of  bones  depends  on  the  different  mechanic 
cal  arrangements  of  the  parts  composing  them. 

11.  The  bones  not  only  constitute  the  frame  work  of  the 
human  fabric,  but  they  also  protect  the  vital  organs,  as  the 
heart  and  lungs,  the  brain  and  spinal  marrow,  and  also  con- 
stitute a  series  of  levers,  by  means  of  which,  through  the 
agency  of  muscles,  locomotion  is  performed.  The  bones  in 
man  also  furnish  cavities  for  the  secure  lodgment  of  the  deli- 
cate organs  of  the  senses,  as  the  orbits  of  the  eye,  ear,  mouth, 
and  nostrils.  In  man,  and  the  higher  order  of  animals,  the 
bones  are  for  the  most  part  in  the  interior  of  the  body,  and 
when  near  the  surface,  as  in  the  skull,  they  are  covered  by 
muscles  or  membranes ;  but  in  the  Crustacea,  insects,  &c.,  the 
bones  compose  an  external  case  within  which  all  the  soft 
parts  are  contained* 

12.  If  we  divide  any  of  the  long  bones  longitudinally,  we  find 
two  kinds  of  structure,  the  hard  or  compact,  and  the  alveolar 
or  spongy.  Indeed  there  is  no  bone  that  does  not  exhibit  to 
some  extent  both  of  these  structures  ;  the  compact  forming 
its  external,  and  the  spongy  its  internal  part.  These  two 
formations  are  clearly  seen  in  the  bones  which  compose  the 
skull,  (as  in  the  following  cut,)  with  the  spongy  or  cancel- 


3    ^^^ 

a.  External  plate.     6.  c.  Internal  plates. 

kted  structure  between  them.     This  will  serve  to  illustrate 
the  structure  of  all  the  flat  bones. 


13.  The  above  cut  represents  a  section  of  the  thigh  bone, 


44  PHYSIOLOGY. 

a.  a.  the  extremities  having  a  shell  or  thin  plate  of  compact 
texture,  crowded  with  small  cells,  diminishing  in  size,  but  in- 
creasing in  number  as  they  approach  the  articulation  ;  c,  the 
cavity  for  containing  the  marrow  ;  b,  b.  the  walls  of  the  shaft 
very  firm  and  solid.  The  compact  part  is  thickest  near  the 
middle  of  the  bone  where  the  greatest  strength  is  required. 
This  structure  admirably  combines  the  greatest  degree  of 
strength,  with  the  least  degree  of  weight  aud  expense  of  ma- 
terial. It  can  be  mathematically  demonstrated  that  the  re- 
sistance of  a  cylindrical  body,  such  as  a  pillar  or  mast,  to  a 
force  applied  transversely  is  increased  in  proportion  to  its 
diameter.  The  same  quantity  of  matter,  therefore,  placed  in 
the  circumference  of  a  circle  produces  a  stronger  bone  than 
if  united  in  the  centre  with  proportionally  diminished  diame- 
ter. 

14.  How  admirably  adapted  is  the  arrangement  of  the 
parts  of  the  long  bones  to  the  purposes  for  which  they  are 
destined.  Their  extremities  are  the  fixed  points  from  which 
the  muscles  re-act,  and  where  greater  space  was  required  for 
the  insertion  of  the  tendons  ;  their  diameter  is  on  this  ac- 
count considerably  increased,  and  their  osseous  matter  is 
disposed  in  nearly  an  equal  degree  through  their  whole  sub- 
stance ;  while  in  the  middle  of  the  bone,  which  is  more 
exposed  to  external  violence,  and  where  nothing  was  want- 
ing but  mere  strength,  the  bony  plates  are  all  consolidated 
together  into  a  compact  dense  ring,  leaving  the  centre 
nearly  hollow. 

15.  While  the  long  bones  of  the  lower  extremities  are 
adapted  for  the  support  of  the  body,  and  its  various  progres- 
sive motions,  those  of  the  upper  extremities  are  equally 
fitted  for  acting  upon  contiguous  bodies,  being  so  attached  to 
the  trunk  as  to  be  easily  applied  to  them  in  all  directions. 

The  flat  bones  on  the  other  hand  offer  an  extensive  sur- 
face of  defence,  as  those  of  the  skull,  or  for  the  origin  and 
insertion  of  muscles,  as  the  shoulder  blade.  The  rounded 
bones  composing  the  spinal  column  and  the  angular  bones  o£ 


STRUCTURl?    OF    THE    HUMAN    BODY.  45 

the  wrist  and  ankle,  have  the  bony  matter  extended  over  a 
considerable  space,  in  order  in  the  most  efficient  manner  to 
combine  the  properties  of  lightness  and  strength.  The 
whole  assemblage  constitutes  an  apparatus  which  is  capable 
of  executing  all  the  various  movements  that  are  necessary  for 
the  purposes  of  life,  with  a  degree  of  precision  and  velocity 
that  is  truly  wonderful. 

16.  The  bones  are  covered  with  a  fibrous  sheathing  of 
dense  membrane,  called  'periosteum,  which  seems  to  nourish 
the  bone,  for  where  it  is  abraded  the  bone  perishes.  It  con- 
tains an  abundance  of  blood-vessels  which  run  from  it  into 
the  bone  ;  besides  these,  a  large  blood-vessel  enters  the  shafts 
of  the  lonoj  bones  near  the  centre,  and  branches  out  in  each 
direction,  while  numerous  others  enter  at  their  extremities. 
These  blood-vessels,  though  generally  too  minute  to  convey 
the  red  particles  of  the  blood,  yet  they  readily  transmit  the 
colouring  matter  of  madder.  Numerous  experiments  have 
proved  that  when  animals  are  supplied  with  food  mixed  with 
that  substance,  in  a  few  days  the  bones  are  coloured  red,  or 
of  a  pinkish  colour,  and  on  the  discontinuance  of  it,  in  a 
short  time  their  natural  colour  is  restored,  showing  the 
rapidity  with  v/hich  deposition  and  absorption  are  carried 
on  in  the  healthy  state.  This  is  shown  in  cases  of  fracture, 
where  the  broken  ends  of  a  bone  become  speedily  united.  I 
have  lately  had  a  case  of  fractured  thigh  bone  in  a  child, 
where  it  became  united  with  considerable  firmness  in  one 
week. 

17.  Marrow  is  a  species  of  fat  deposited  in  the  central 
canals  of  the  cylindrical  bones,  and  in  the  lattice  work  of 
the  spongy  bones.  It  is  contained  in  the  cells  of  a  delicate 
membranous  web,  and  has  been  supposed  by  some  to  serve 
as  a  reservoir  of  nourishment,  and  by  others,  to  keep  the 
bones  from  becoming  dry  and  brittle.  It  is  found  in  greater 
quantity  in  the  adult  and  aged  than  in  the  young  ;  in  the 
latter,  indeed,  its  place  is  occupied  by  a  gelatinous  fluid. 

18.  Chemical  examination  shows  that  bone  is  composed 


46  PHYSIOLOGY. 

of  earthy  aud  animal  matter,  the  former  constituting  about 
two-thirds,  the  remaining  one-third  being  animal  matter. 
As  we  find  portions  of  both  these  substances  in  the  minutest 
particles  of  bones,  both  are  therefore  considered  essential  to 
its  composition,  and  existing  in  a  state  of  chemical  union, 
and  not  as  a  mere  mechanical  mixture.  These  two  sub- 
stances can  be  readily  separated  from  each  other.  If  we 
immerse  bones  for  some  time  in  diluted  nitric  acid,  or  muri- 
atic acid,  though  they  retain  their  size  and  form,  their 
weight  is  considerably  diminished,  and  they  are  rendered 
soft,  pliable,  and  elastic.  The  earthy  portion,  phosphate  of 
lime,  has  been  dissolved,  and  is  held  in  solution  in  the  fluid, 
and  the  animal  portion,  gelatine,  remains  uninjured. 


Membranous,  or  gelatinous  portion  of  bone  ;  the  earthy  portion  being- 
60  completely  removed^  that  it  is  capable  of  being  tied  in  a  knot. 

19.  If  bones  are  subjected  to  a  strong  heat,  as  in  a  char- 
coal fire,  on  cooling  they  appear  to  have  undergone  no  alter- 
ation in  figure  or  bulk  ;  but  they  are  rendered  white  as 
chalk  ;  their  weight  is  lessened,  and  they  become  very 
brittle.  In  this  case,  the  animal  matter  has  been  wholly 
consumed  by  the  fire,  while  the  earthy  part  remains  un- 
changed ;  in  the  former  case,  the  very  reverse  happened ; 
the  animal  matter  remaining,  and  the  earthy  being  removed^ 

3* 


STRUCTURE    OF    THE    HUMAN   BODY. 


47 


Earthy  portion  of  bone. 


20.  The  proportion  between  the  animal  and  earthy  sub- 
stances varies  in  different  individuals,  and  in  the  same  indi- 
vidual at  different  periods  of  life,  and  under  various  condi- 
tions of  health.     In  youth,  the  former,  in  old  age,  the  latter 
predominates.     The  earthy  matter  is  sometimes  so  deficient 
that  the  bones  have  not  the  necessary  degree  of  firmness 
and  rigidity.     The  consequence  is,  that  those  parts  of  the 
skeleton   which  have  to  support  any  considerable  weight 
bend  under  it,  as  the  spine,  the  bones  of  the  pelvis,  and  the 
lower  limbs.     This  is  one  cause  of  spinal  distortions,  though 
they  are  generally  caused  by  debility  of  the  muscles  from 
want  of  proper  exercise.     In  many  cases  of  the  former  kind, 
by  the  subsequent  deposition  of  earthy  matter,  the  bones  be- 
come  sufficiently  dense   and  compact ;    but  the  distortion 
remains  fixed  and  permanent,  and  mechanical  means,  such 
as  pulleys,  screws,  inclined  planes,  &c.,  only  serve  to  torture 
the  patient,  without  affording  the  slightest  prospect  of  a 
cure.     No  one  who  understands  physiology  will  attempt  to 
correct    such  distortions   by  mechanical    means.      Where 
there  is  a  deficiency  of  animal  matter,  the  bones  want  a 
poper  degree  of  tenacity,  and  are  therefore  easily  fractured 
by  slight  blows  or  falls. 

21.  The  ends  of  the  bones  which  are  used  for  motion,  as 
already  mentioned,  are  tipped  with  cartilage  or  gristle,  which 
is  very  smooth  and  hard  ;  and  it  is  constantly  wet,  in  a  state 
of  health,  by  a  fluid  which  answers  the  same  purpose  as  oil 
in  machinery,  or  tar  upon  wagon  wheels.     The  joints  are 


48  PHYSIOLOGY. 

enclosed  in  membranous  bags,  and  in  health  the  fluid  which 
moistens  them  is  of  just  the  right  quantity  and  quality  ;  but 
if  we  do  not  take  proper  exercise,  or  if  we  take  food  or  drink 
that  is  too  heating  or  irritating,  the  joints  grow  stiff,  or 
rheumatism  oV  gout  may  be  the  consequence. 

22.  In  those  parts  where  bones  are  to  be  formed,  a  mould  of 
gristle  or  cartilage  is  first  deposited,  of  the  exact  shape  that 
the  future  bone  is  to  take  ;  and  as  bony  particles  are  secret- 
ed by  the  blood,  the  cartilage  is  taken  up  by  the  absorbent 
vessels.  In  the  long  round  bones,  this  process  begins  in  the 
middle,  and  in  the  flat  bones,  like  the  shoulder  blade,  or  those 
of  the  skull,  it  begins  in  the  centre  and  extends  gradually 
towards  the  circumference.  But  in  the  skull,  all  the  bones 
are  not  completely  formed,  till  several  months  after  birth. 

23.  The  bones  are  variously  connected  by  joints  or  arti- 
culations, which  admit  of  different  degrees  of  motion,  both 
in  extent  and  variety.  Some  of  these  connections  allow 
free,  easy,  and  conspicuous  motion,  as  the  shoulder  and  hip 
joints,  which  are  called  hall  and  socket  joints  ;  in  others, 
there  is  motion  in  only  two  directions,  as  the  knee,  elbow, 
wrist,  and  ankle.  These  are  called  hinge-joints,  from  their 
resemblance  to  a  hinge.  Some  bones,  like  those  of  the  skull, 
though  connected  by  a  kind  of  articulation,  are  nevertheless 
immoveable. 

24.  Another  form  of  animal  matter,  differing  essentially 
from  those  we  have  been  considering  is,  muscular  tissue. 
This  is  familiar  to  all  under  the  name  o^  Jlesh,  It  is  a  sub- 
stance  of  a  peculiar  nature,  arranged  in  fibres  of  extreme 
delicacy.  It  is  distinguished  from  every  other  texture  in 
the  body,  by  an  innate  power  of  contraction  ;  on  examin- 
ing it  with  microscopes  of  great  magnifying  power,  it  is 
found  to  be  composed  of  filaments  so  fine  as  the  one  forty 
thousandth  part  of  an  inch  in  dianieter.  These  filaments 
collected  together,  form  fibres,  which  are  plainly  perceptible 
in  boiled  flesh.  A  collection  of  these  fibres  form  a  bundle, 
and  these  bundles  collectively  constitute   a   muscle ;   and 


STRUCTURE    OF    THE    HUMAN    BODY. 


49 


muscles  appear  coarse  or  fine  according  to  the  size  of  these 
bundles. 

25.  These  fibres  appear  to  be  very  uniform  as  to  shape, 
size,  and  general  appearance,  being  delicate,  soft,  flattened, 
and  though  consisting  only  of  a  tender  pulp,  still  solid.  The 
fibrous  and  fascicular  arrangement  appears  to  be  chiefly  con- 
fined to  muscles  of  voluntary  action,  as  they  are  scarcely 
perceptible  in  the  heart,  and  not  at  all  in  the  alimentary 
canal,  or  urinary  bladder.  In  the  stomachs  of  birds,  how- 
ever, the  fibrous  structure  is  very  distinct,  especially  in 
hawks  and  owls. 


The  appearance  of  the  ultimate  fibres  and  of  their  transverse  lines,  as 
seen  under  the  microscope  of  Mr.  Lister,  when  the  object  is  magnified 
500  diameters. 

26.  The  muscular  fibres  are  every  where  penetrated  by 
cellular  tissue  and  numerous  blood-vessels  and  nerves.  The 
colour  of  the  muscle  of  course  varies,  according  to  the  quan- 
tity and  quality  of  the  blood.  In  adult  animals  it  is  of  various 
shades  of  red  ;  in  young  animals,  of  a  cream  colour,  as  in 
veal ;  in  birds,  it  varies  in  different  muscles  ;  in  fowls,  for 
example,  it  is  white  on  the  breast,  and  a  deep  brown  on  the 
legs  ;  while  in  fishes,  it  is  bluish,  or  white,  &;c. 

27.  No  part  of  the  body  except,  perhaps,  the  organs  of 
sense,  is   so   abundantly   supplied    with   blood-vessels    and 

5 


50 


PHYSIOLOGY. 


Berves,  as  the  muscular  tissue.  There  is  reason  to  beheve 
that  every  filament,  however  fine,  is  provided  with  the  ulti- 
mate branch  of  an  artery,  vein,  and  nerve.  The  direction 
of  the  fibres  of  muscles  varies  ;  in  some,  being  parallel ;  in 
others,  radiating  in  different  directions.  In  some  instances,- 
they  form  nearly  or  quite  a  circle,  as  the  muscle  which 
closes  the  eye,  and  those  of  the  intestinal  canal ;  in  others, 
they  are  penniform,  or  having  their  fibres  disposed  like  those 
forming  the  feathery  part  of  a  quilL 


Two  portions  of  muscle  ;  one  of  which,  a,  is  covered  with  mem- 
brane ;  the  other,  6,  is  uncovered  ;  e,  the  muscular  fibres  terminating  in- 
tendon. 


27.  Muscular  tissue  is  supposed'  to  consist  chiefly  of 
fibriuy  though  some  chemists  state  that  it  contains  albumen, 
gelatine,  and  osmazome.  These  latter  substances  however, 
are  probably  obtained  from  the  cellular  tissue  which  encloses 
and  dips  down  between  the  fibres  of  muscles.  Fibrin  con- 
tains a  larger  proportion  of  azote,  the  element  peculiar  to  the 
animal  body,  than  any  other  animal  substance.  The  flesh^ 
of  young  animals  affords  a  large  proportion  of  gelatine,  while' 


STRUCTURE    OF    THE    HUMAN    BODY.  51 

it  is  deficient  in  fibrin — in  adult  animals,    the    fibrin  pre- 
dominates, and  the  gelatine  is  deficient. 

28.  The  pecuhar  property  of  muscular  tissue  is  vital,  and 
consists  in  the  power  of  diminishing  its  length,  or  shortening 
on  the  application  of  stimulus.  All  the  motions  of  the  body 
are  performed  by  means  of  it,  and  without  its  incessant 
action,  respiration,  digestion,  nor  circulation  could  be  carried 
on  for  a  moment.  Tendons,  ligaments,  cartilages,  and  bones 
seem  to  be  mechanical  contrivances  to  aid  the  muscles  in 
accomplishing  their  varied  purposes,  so  that  the  only  source 
of  motion  in  the  body  is  muscular  tissue,  and  the  only  mode 
in  'svhich  motion  is  generated  is  by  contractility. 

29.  The  last  primary  tissue  which  we  have  to  describe,  is 
termed  nervous.  It  consists  of  a  soft  and  pulpy  matter,  of  a 
brownish  white  colour,  and  appears  to  be  composed  of  solid, 
elongated  threads,  differing  in  thickness  from  that  of  a  hair 
to  the  finest  fibre  of  silk.  Like  the  muscles^  the  nerves  are 
enclosed  in  a  sheath  of  condensed  cellular  membrane,  called 
neurilema,  or  nerve  coat ;  and  like  them  also,  each  nerve  is 
composed  of  many  bundles  ;  these  of  many  fibres  ;  and  the 
fibres  of  many  filaments.  In  one  respect  the  nervous  fibres 
differ  from  the  muscular,  and  that  isy  while  the  muscular  fi- 
bres generally  run  parallel  to  each  other,  those  of  the  nerves 
cross  and  penetrate  each  other,  so  as  to  form  an  intimate  in- 
terlacement, as  represented  on  the  following  page.  When  we 
come  to  describe  the  vascular  system,  it  will  be  seen  that 
either  all  the  vessels  proceed  from  one  large  trunk,  which 
goes  on  progressively  to  divide  and  subdivide,  until  its 
branches  become  so  minute  as  to  be  invisible  ;  or  that  they 
arise  by  numerous  and  invisible  branches,  which  unite  to 
form  larger  and  larger  vessels,  until  they  ultimately  consti- 
tute  only  a  few  trunks.  But  the  muscular  and  nervous  fila- 
ments never  divide  and  subdivide  in  this  manner.  It  is  the 
opinion  of  the  best  anatomists,  that  there  is  a  diameter  be- 
yond which  they  no  longer  diminish.  That  diameter  they 
maintain  is  quite  uniform  in  each. 


52 


PHYSIOLOGY. 


Nervous  fibres,  deprived  of  their  neurilema  and  unravelled,  showing 
the  smaller  threads,  or  filaments,  of  which  the  fibres  consist. 

30.  The  nervous  tissue  is  also  abundantly  supplied  with 
blood-vessels,  like  the  muscular  ;  so  that  there  is  not  a  fibre 
or  filament,  however  minute,  which  is  not  supplied  by  a  dis- 
tinct blood-vessel.     The  nervous  structure  forms  the  brain. 


STRUCTURE    OF    THE    HUMAN    BODY. 


53 


spinal  marrow,  nerves  and  their  ganglions.  The  nervous  tis- 
sue appears  to  consist  of  two  substances,  which  as  far  as  the 
eye  can  distinguish,  appear  to  be  entirely  distinct  from  each 
other.  The  one  is  called  cineritious,  or  gray,  from  its  col- 
our ;  from  its  position,  cortical,  and  from  its  consistence  pulpy. 
This  last  appears  to  be  composed  chiefly  of  blood-vessels. 
The  other  is  termed  white,  or  medullary.  It  is  of  firmer 
consistence  than  the  pulpy.  This  is  decidedly  fibrous  in  its 
nature.  In  every  part  of  the  nervous  system  which  consti- 
tutes a  distinct  nervous  apparatus,  both  substances  are  con- 
joined. Neither  the  pulpy,  nor  the  fibrous  alone,  forms  a 
distinct  organ  ;  the  union  of  both  is  necessary  to  constitute 
an  instrument  capable  of  performing^  a  specific  function. 


TJItimate  fibres  of  nerve  highly  magnified  ;  showing  the  strings  of 
•globules  of  which  they  consist. 

31.  Much  controversy  exists  in  relation  to  the  shape  of 
the  ultimate  particles  of  nervous  matter  ;  but  while  micro- 
scopical observations  difier  as  much  as  they  have  done  hith- 
erto, the  question  may  fairly  be  considered  as  unsettled. 
The  common  opinion  is,  that  the  ultimate  filaments  of  which 
they  are  composed,  ai*e  formed  of  globules  of  extreme  minute- 
ness. But  then,  when  we  consider  the  peculiar  difficulties 
attending  investigations  of  this  nature,  that  they  require  un- 
wearied perseverance,  extreme  accuracy,  great  patience,  and 
a  dexterity  with  the  hand,  united  with  a  delicate  discrimina- 
tion  of  the  eye,  that  belong  to  few:,  and  when  we  consider 

moreover,  that  these  very  endowments  can  only  be  acquired 

5* 


54 


PHYSIOLOGY. 


by  long  practice,  we  shall  be  led  to  pause,  before  we  adopt 
the  opinions  of  every  microscopical  enthusiast  who  enters  on 
this  very  extensive,  and  deeply  fascinating  field  of  discovery. 


Portion  of  the  trunk  of  a  nerve  dividing  into  two  branches. 


Questions. — Describe  the  fibrous  structure.  What  are  its  uses? 
What  are  ligaments  ?  What  is  a  capsular  ligament  ?  What  use  do 
ligaments  serve  ?  "When  sprained,  what  is  a  good  remedy  ?  What  is 
a  tendon  or  sinew  ?  Where  are  they  found  ?  What  their  use  ?  Of 
what  composed  ?  Have  they  much  sensibility  ?  Why  are  bones 
sometimes  placed  in  a  tendon  ?  What  use  does  the  knee-pan  serve  ? 
Describe  the  cartilaginous  tissue.  What  are  its  uses  ?  How  may  its 
structure  be  shown  ?  What  is  the  elastic  tissue  ?  Where  is  it  found  ? 
What  are  its  uses  ?    What  constitutes  the  most  solid  portion  of  the  sys- 


STRUCTURE    OF    THE    HUMAN    BODY.  55 

tem  ?  What  are  the  uses  of  the  bones  ?  How  many  are  there  in  the 
human  skeleton  ?  Is  bone  supplied  with  blood-vessels  ?  What  is  the 
different  density  of  bones  owing  to  ?  What  situation  do  the  bones 
occupy  in  man  ?  In  the  Crustacea  and  insects  ?  Describe  the  structure 
of  the  long  bones  ? — of  the  flat  bones  ?  What  is  the  chief  use  of  the 
flat  bones  ?  What  covering  have  the  bones  ?  What  is  the  structure 
of  the  periosteum  ?  What  its  use  ?  How  are  the  bones  nourished  ? 
What  effect  has  madder  upon  bones  when  taken  internally  ?  What  is 
marrow  ?  Where  is  it  deposited  ?  What  its  use  ?  At  what  period  of 
life  is  it  most  abundant  ?  What  is  the  composition  of  bone.  What  pro- 
portion  is  animal  matter  ?  What  earthy  ?  How  are  these  different  sub- 
stances shown  ?  Are  their  proportions  affected  by  age  or  health  ? 
What  is  the  consequence  when  the  earthy  matter  is  deficient  ?  What 
when  the  animal  ?  How  are  spinal  distortions  best  remedied  ?  How 
is  bone  formed  ?  Are  all  the  bones  formed  at  the  time  of  birth  ?  What 
is  muscular  tissue  ?  By  what  property  is  it  distinguished  ? — Of  what 
composed  ?  What  are  fibres  ?  What  bundles  ?  How  do  the  fibres 
appear?  Do  all  muscles  possess  the  fibrous  arrangement?  To  what  is 
the  colour  of  muscle  owing  ?  Of  what  colour  is  the  muscle  of  fishes  ? 
Of  what  shape  are  muscles  ?  What  is  the  chemical  composition  of 
muscular  tissue  ?  Does  age  affect  the  quantity  of  fibrin  in  animals  ? 
What  peculiar  property  does  muscular  fibre  possess  ?  What  its  use  ? 
Describe  the  nervous  tissue.  What  is  the  neurilema  ?  Does  nervous 
tissue  abound  with  blood-vessels  ?  What  does  it  form  ?  How  many 
kinds  of  substance  is  contained  in  it  ?  What  is  the  cineritious  ?  What 
their  cortical  portion  ?  Does  either  alone  form  any  organ  ?  What  is 
said  of  the  shape  of  the  ultimate  paj-ticles  of  matter  ? 


CHAPTER  V. 

CHEMISTRY    aF    THE    HUMAN    BODY. 

Ultimate  and  Chganic  Elements. 

1.  By  the  chemiec^  composition  of  the  body,  is  meant 
those  ultimate  elements  of  which  it  is  made  ;  such  as  oxygen, 
carbon,  hydrogen,  and  azote.  By  the  organic  composition, 
we  mean  the  proximate  elements,  which  are  formed  out  of 
these  by  the  power  of  the  living  principle  ;  such  as  albumen, 
Jibrin,  gelatine,  &;c, 

2.  The  ultimate  elements  of  animal  matter  have  been 
divided  into  non-metalUc,  and  metallic  substances  ;  the  former 
consisting  of  oxygen,  hydrogen,  carbon,  azote,  phosphorus^ 
sulphur,  chlorine,  and  fluorine  ;  the  latter,  1,  the  bases  of  the 
alkalies,  viz.,  potassium,  sodium,  nnd  calcium;  2,  the  bases 
of  the  earths,  magnesium,  silicium,,  and  aluminum ;  3,  the 
ponderous  metals,  iron,  mangajiese,  and  copper. 

Of  the  first  class,  or  the  non-metallic  substances,  oxygen, 
hydrogen,  carbon  and  azote  exist  in  much  the  largest  pro- 
portion, and  are  in  fact  the  only  essential  elements  of  animal 
matter. 

3.  All  the  solids  and  fluids  of  the  body  contain  oxygen. 
It  is  essential  to  all  the  proximate  elements.  United  with 
hydrogen,  it  forms  water,  which  is  calculated  to  constitute 
nine-tenths  of  the  whole  weight  of  the  body.  In  union  with 
carbon,  it  forms  carbonic  acid,  which  exists  in  the  blood,  and 
is  thrown  out  by  the  lungs  and  skin. 

3.  Oxygen  forms  with  phosphorus,  phosphoric  acid,  which 
with  lime  constitutes  the  earthy  portion  of  the  bones  ;  it  also 
exists  in  some  of  the  secretions.  In  union  with  their  metalic 
l:«ises,  it  forms  potash,  soda,  a.ndUme.     It  also  is  a  consti- 


CHEMISTRY    OF    THE    HUMAN    BODY.  57 

tuent  part  of  albumen,  fibrin,  gelatine,  and  mucus.  Oxygen 
is  derived  partly  from  the  air  we  breathe,  and  partly  from 
our  food  and  drinks.  It  is  given  off  in  all  the  secretions 
and  excretions.  The  air  contained  in  the  swimming  bladder 
of  fishes,  is  pure  oxygen. 

4.  Hydrogen  exists  in  all  the  fluids  and  most  of  the  solids, 
constituting  as  it  does  one  element  of  water.  In  venous 
blood,  it  exists  in  a  larger  proportion  than  in  arterial  blood, 
which  contains  more  oxygen.  In  the  bile,  it  is  very  abund- 
ant, and  in  fat  and  oil,  is  one  of  the  essential  elements.  It 
is  this  gas  which  often  causes  so  much  distress  in  a  weak 
state  of  the  stomach.  Hydrogen  is  introduced  into  the 
system  by  means  of  food  and  drinks,  and  is  discharged  in 
the  same  manner  as  oxygen. 

5.  Carbon  abounds  in  the  vegetable  as  well  as  animal 
kingdom.  In  oil,  fat,  albumen,  gelatine,  fibrin,  and  mucus, 
it  always  forms  a  part.  In  bile,  and  in  venous  blood,  it 
exists  largely.  If  we  burn  a  piece  of  animal  substance, 
what  is  left  is  found  to  be  chiefly  carbon.  We  obtain  it 
from  nnr  foofl,  and  give  it  off  by  breathing  and  the  secretions. 
It  is  carbon  that  makes  venous  blood  darker  than  arterial, 
and  the  change  from  purple  to  bright  crimson  which  takes 
place  in  the  lungs,  is  supposed  to  be  owing  chiefly  to  the 
fact,  that  the  excess  of  carbon  contained  in  venous  blood  is 
discharged  by  respiration. 

6.  Azote  exists  in  large  quantities  in  all  animal  matter. 
It  also  exists  to  some  extent  in  a  few  vegetables,  but  it  is  an 
essential  element  in  animal  substances.  It  is  more  abund- 
ant in  fibrin,  of  which  the  muscular  flesh  is  chiefly  formed, 
than  in  any  other  portions  of  the  body,  though  it  is  found 
in  the  brain  and  nerves.  The  peculiar  smell  of  burning 
animal  matter  is  owing  to  azote.  When  animal  substances 
putrefy,  it  combines  with  hydrogen,  and  forms  ammonia  or 
hartshorn. 

7.  Azote  is  chiefly  taken  into  the  system  by  means  of 
animal  food.     It  is  also  taken  into  the  blood  by  respiration, 


-58  PHYSIOLOGY. 

as  it  forms  a  constituent  part  of  the  atmosphere.  This, 
however,  is  denied  by  some  chemists.  It  is  discharged  from 
the  system  in  the  same  manner  as  oxygen,  hydrogen,  and 
carbon  ;  though  chiefly  through  the  kidneys. 

8.  Phosphorus  exists  both  in  animal  and  vegetable  sub- 
stances. Nearly  every  part  of  animal  bodies  contain  it, 
though  it  is  found  more  abundantly  in  the  bones.  It  gener- 
ally exists  in  combination  with  oxygen,  forming  'phosphoric 
acid.  It  is  discharged  mostly  through  the  kidneys.  The 
spontaneous  combustion  of  human  bodies,  of  v/hich  we  have 
some  well-attested  cases  of  drunkards,  is  supposed  to  be  owing 
to  an  accumulation  of  phosphorus  in  the  system,  from  some 
unknown  cause. 

9.  Sulphur  is  always  united,  in  animal  substances,  with 
other  elements,  as  soda  and  potash.  It  is  found  in  albiunen, 
in  the  hair  and  nails,  and  in  muscidar  jlesh.  It  is  given  off 
by  the  intestines  and  by  the  skin. 

10.  Chlorine  is  found  in  most  of  the  animal  fluids  com- 
bined with  hydrogen.  This  forms  hydrochloric  acid.  In 
the  blood  it  is  combined  with  sorla  nnrl  pnta>h.  It  i«  found 
also  in  the  gastric  juice,  in  sv)eat,  milk,  saliva,  &;c. 

11.  Potash  exists  more  abundantly  in  plants  than  in  ani- 
mals. It  is,  however,  contained  in  the  hlood,  bile,  urine, 
sweat,  milk,  &c. 

12.  Soda  is  more  abundant  in  animals  than  plants.  It 
exists  in  the  same  fluids  in  which  potash  is  found  ;  also  in 
bones  and  muscular  flesh.  It  is  always  combined  with  some 
acid. 

13.  Lime  forms  a  large  part  of  the  bones,  in  union  with 
phosphoric  or  carbonic  acid.  Silex  exists  in  human  hair, 
and  in  some  of  the  secretions.  Magnesia  is  contained  in 
bones,  and  in  some  animal  fluids,  as  milk.  It  is  also  found 
in  the  brain.  Iron  forms  the  colouring  principle  of  the  red 
globules  of  the  blood,  and  is  therefore  pretty  extensively 
ibund  in  animal  bodies. 


CHEMISTRY    OF    THE    HUMAN    BODY  59* 

14.  The  organic  or  'proximate  elements  of  the  body  are 
formed  from  the  ultimate  elements  already  described.  We 
cannot  explain  their  formation  on  any  chemical  or  mechan- 
ical  laws,  but  refer  them  solely  to  the  influence  of  the  vital 
forces. 

15.  These  proximate  elements  are  mostly  formed  from  a 
combination  o^  oxygen,  carbon,  hydrogen,  and  azote,  and  are 
divided  into  two  classes,  acids  and  oxyds. 

16.  The  acids  found  in  the  human  S5^stem  are  the  acetic, 
oxalic,  the  benzoic,  and  the  uric.  The  three  first  are  also 
found  in  the  vegetable  kingdom,  and  are  composed  of  oxygen, 
hydrogen,  and  carbon.  When  these  organic  elements  are 
made  of  three  simple  elements,  they  are  called  ternary 
oxyds ;  such  are  sugar,  resin,  and  the  jixed  and  volatile 
oils, 

17.  Milk  contains  a  considerable  quantity  of  sugar.  It 
can  be  obtained  from  whey  by  evaporating  it  slowly  to  the 
consistence  of  a  syrup,  and  then  allowing  it  to  cool.  It  may 
then  be  purified  by  the  white  of  an  Ggg,^  or  albumen,  and 
crystalized  again.  It  has  a  different  taste  from  the  sugar 
of  the  cane. 

18.  The  bile  contains  a  peculiar  resin.  Fat  and  the  mar- 
row of  the  bones  contain  fixed  oils.  But  the  most  important 
compounds  of  the  body  ai'e  albumen,  fibrin,  gelatine,  mucu^s,. 
and  osmazome. 

19.  Alhmnen  exists  in  the  body,  both  in  a  solid  and  fluid 
form.  Combined  with  water  it  forms  the  white  of  eggs  ;■ 
hence  its  name.  It  exists  most  abundantly  in  the  senim, 
but  is  found  in  all  the  fluids  of  the  body.  It  is  transparent, 
without  colour^  taste,  or  smell,  and  coagulates  by  heat,  acids, 
and  alcohol.. 

20.  Solid  albumen  is  also  a  white  and  tasteless  substance.. 
It  forms  the  basis  of  the  nerves  and  brain,  and  is  contained 
in  the  shin,  hair,  nails,  glands,  and  vessels.  Tumours  and 
wens  are  mostly  composed  of  albumen.     It  is  composed  of 


60  PHYSIOLOGY. 

Carbon  52  parts ;  Oxygen  23  parts ;  Hydrogen  7  parts ; 
Azote  15  parts. 

21.  Fibrin  is  the  basis  of  muscular  flesh  ;  and  enters 
largely  into  the  formation  of  the  blood,  cliyle,  and  lymph.  It 
is  owing  to  the  presence  of  fibrin  that  blood  coagulates  when 
removed  from  the  body.  Fibrin  is  a  solid,  white  substance, 
of  a  fibrous  structure,  destitute  of  smell  and  taste,  and  in- 
soluble in  water. 

22.  Fibrin  may  be  obtained  by  washing  the  thick  part  of 
the  blood  with  cold  water,  and  thus  separating  the  colouring 
matter,  or  the  red  globules.  It  differs  from  albumen  by 
possessing  the  property  of  coagulating  at  all  temperatures. 
Fibrin  is  composed  of  Carbon  43  "parts  ;  Oxygen  19  parts  ; 
Hydrogen  7  parts;  Azote  19  pai'ts.  It  contains  more  azote 
and  less  oxygen  than  albumen. 

23.  Gelatine  is  found  in  none  of  the  fluids  of  the  human 
body.  It  is,  however,  found  in  nearly  all  the  solids.  It  is 
known  from  all  the  other  animal  principles  by  its  readily 
dissolving  in  warm  water,  forming  a  kind  of  jelly.  When 
dry,  it  forms  a  hard,  shining,  brittle  substance,  called  glue. 
This  is  mostly  prepared  from  the  skins  and  hoofs  of  animals, 
by  boiling  them  in  water,  and  then  evaporating  the  solution. 
Isinglass  is  obtained  from  the  sounds  of  the  sturgeon,  and  is 
a  very  pure  gelatine. 

24.  Gelatine  exists  largely  in  the  skin,  cartilages,  liga- 
ments, tendons,  and  bones,  and  it  forms  the  basis  of  the 
cellular  tissue.  As  it  does  not  exist  in  the  blood,  it  is  pro- 
bably a  modification  of  albumen.  It  is  composed  of  Carbon 
47  parts  ;  Oxygen  27  parts  ;  Hydrogen  7  parts  ;  Azote  16 
parts. 

25.  It  appears  that  gelatine  contains  less  carbon  than 
albumen,  by  5  or  6  per  cent.,  and  a  larger  proportion  of 
oxygen  in  the  same  ratio.  Now,  if  we  suppose,  that  near 
the  skin,  and  in  the  various  tissues  of  the  body,  the  albumen 
of  the  blood  gives  off*  a  portion  of  its  carbon,  a  part  of  which 


CHEMISTRY     OF      THE    HUMAN    BODY.  61 

is  taken  up  by  the  veins,  and  a  part  thrown  off  by  the  skin, 
Jungs,  and  various  secretions,  we  shall  see  how  gelatine  may 
be  formed  out  of  albumen. 

26.  Osmazome  is  an  element  which  exists  in  all  the  animal 
fluids,  and  in  some  of  the  solids,  as  the  brain  and  muscular 
Jihre.  It  is  of  a  reddish  brown  colour,  of  an  aromatic  smell 
and  agreeable  taste.  It  is  this  which  gives  the  strong  flav- 
our of  roasted  meat,  and  the  peculiar  taste  of  the  various 
kinds  of  animal  food.  It  is  supposed  to  be  tonic  and  stimu- 
lating, but  to  possess  no  nutritive  properties. 

27.  Mucus  is  that  bland  fluid  which  moistens  the  surface 
of  all  the  mucous  membranes.  In  some  of  the  hard  parts 
of  the  body,  which  are  destitute  of  sensibility,  it  is  found  to 
exist  in  considerable  quantities,  as  in  the  nails,  hair,  and 
cuticle  of  man,  and  in  the  scales,  feathers,  and  wool  of  dif- 
ferent animals.  That  part  of  the  skin  called  rete  mucoscum, 
is  supposed  to  be  compacted  mucus.  Mucus  is  transparent, 
has  no  colour  or  taste,  and  has  a  ropy  and  viscid  consist- 
ence. When  dry,  it  is  insoluble  in  water.  It  contains 
much  azote» 

28.  There  are  some  other  substances  found  in  the  human 
body,  such  as  caseinef  or  that  principle  of  the  milk  which 
forms  the  basis  of  cheese,  curd,  dec.  ;  but  they  are  not  of 
sufficient  importance  to  need  a  particular  description. 


Questions. — ^What  is  meant  by  the  chemical  composition  of  the 
body  ?  What  are  some  of  the  ultimate  elements  ?  What  are  some 
of  the  proximate  elements  ?  How  have  the  ultimate  elements  been 
divided  ?  Is  oxygen  essential  to  all  the  proximate  elements  ?  What 
is  said  of  hydrogen  ? — Of  carbon  1 — Of  Azote  ?  How  do  oxygen, 
hydrogen,  and  azote  get  into  the  system  ?  Is  phosphorus  found  in 
animal  bodies  ?  What  other  elements  are  met  with  in  animals  ?  How 
are  the  organic  elements  of  the  body  formed  ?  How  divided  ?  What 
acids  are  found  in  animal  bodies  ?  What  are  the  most  important 
compounds  in  the  body  ?  What  is  said  of  albumen  ?  In  what  is  it 
found  ?    What  is  fibrin  the  basis  of?    How  may  it  be  obtained  from 

6 


62  PHYSIOLOGY. 

blood  ?  Of  what  is  it  composed  ?  Where  is  gelatine  found  in  the 
animal  body  ?  How  known  from  the  other  animal  principles  ?  What 
does  it  form  when  dried  ?  Of  what  is  glue  prepared  ?  In  what  does 
gelatine  exist  ?  How  may  we  account  for  the  productions  of  gela- 
tine  ?  What  is  osmazome  ?  What  peculiar  properties  has  it  ?  What 
is  mucus  ?  AVhere  found,  what  is  its  use  ?  Are  any  other  substances 
found  in  the  human  body  ? 


CHAPTER  VI. 


THE    HUMAN    SKELETON. 


1.  Of  all  the  wonderful  works  of  the  great  Architect,  none 
bears  such  convincing  proofs  of  divine  wisdom  and  good- 
ness as  the  mechanism  of  the  human  body.  Every  part, 
down  to  the  minutest  fibre  or  blood-vessel,  bears  the  impress 
of  the  Creator's  hand,  and  the  marks  of  design  and  contri- 
vance  are  so  obvious  throughout,  as  to  lead  the  mind  irre- 
sistibly to  an  all-vvise,  Omnipotent  designer  ! 

2.  The  human  skeleton  consists  of  about  252  bones,  in- 
cluding the  sesamoid,  the  teeth,  and  the  small  bones  of  the 
ear  ;  though  they  are  generally  reckoned  at  211.  They  are 
divided  into  those  of  the  head,  trunk,  and  extremities,  some 
of  them  being  single,  others  in  pairs.  When  the  bones  com- 
posing the  skeleton  are  connected  together  by  natural  liga- 
ments, they  form  what  is  called  a  natural  skeleton ;  when  by 
wires,  it  is  termed  an  artificial  skeleton.  The  latter  is  the 
common  and  most  useful  mode  of  articulation  to  the  anato- 
mist,  as  the  joints  can  be  easily  moved  and  examined.  The 
skeleton  has  been  called  the  bony  frame  work  of  the  body, 
because  by  its  form  and  solidity,  it  not  only  retains  every 
part  of  the  fabric  in  its  proper  shape,  but  also  affords  a  hard 
surface  for  the  attachment  of  muscles,  and  the  protection  of 
many  important  organs.  If  we  suppose  a  plane  to  pass 
down  from  the  top  of  the  head  through  the  middle  of  the  skele- 
ton, the  latter  will  be  divided  into  two  equal  portions,  called 
the  right  and  left  side  of  the  body,  which  are  perfectly  alike 
in  shape  and  size.  Those  bones  which  are  situated  in  the 
centre,  such  as  the  spine  and  breast  bone,  and  are  inter- 
sected by  it,  are  said  to  be  symmetrical,  because  they  are 
divided  equally  ;  the  others,  such  as  the  bones  of  the  arm 
and  leg,  are  in  pairs. 


64 


PHYSIOLOGY. 


THE    HUMAN    SKELETON. 


65 


.■3.  The  bones  of  the  head  are  55  in  number,  as  follows : 

Frontal,  (Os  Frontis,  a,)  ...  1 

Parietals,  (OssaParietalia,  i»,)  .  .  2 

Temporal  .....  2 

Occipital,  (Os  Occipitis)  ...  1 

Sphenoidal,  (Os  Sphenoides,  d,)         ,  .  1 

Ethmoid,  (Os  Ethmoides)        ...  1 

Nasal,  (Ossa  Nasi,  e,)  .  .  .  .  2 

Malar,  (Ossa  malarum  /,)      .  .  .  2 

Lachrymal,  (Ossa  Lachrymalia,)      .  .  2 

Upper  Jaw  bones,  (Ossa  maxillaria  superiora)  2 

Palate  bones,  (Ossa  palatina)  .  .  2 

Inferior  turbinated  bones,  (Ossa  turbinata)  .  2 

Vomer,    ......  1 

Lower  Jaw,  (Os  maxillare  inferius.,  A,)        ,  1 

Teetli,  (Denies)  .  ..  ,  ,  32 

Tongue  bone  (Os  hyoides'i     ,  -.  _1 

Total,  55  55 

To  these  are  sometimes  added  the  proper  bones  of  the  ear,  contained  In  the  tempo- 
ralbones.  « 

Mallei,  (hammer)     .  2 

Incudes,  (anvil)        .  2 

Stapedes,  (stirrup)  .  2 

Orbicularia,  (round  bones)  2 

Total,  ~i  8 

'4.  The  trunk  contain&57  bones,  viz: 

Vertebrse,  (or,)  .  .24 

Ribs,  Costffi,  e,  /,  ^,)  .  24 

Breast  bone,  (Sternum,  c,  d,)  2 

Hip  bones,  (Ossa  innominata,  i,)     2 
!Riimp  bones,  (Os  sacrum,  k,)  1 

Coceygeal  bones,  (Ossa  coceygis)    4 


Total,  57 

•5.  The  upper  extremities  contain  68  bones,  viz : 

Collarbones,  (Claviculae,  a,)  .  .  2 

Slioulder  blades,  (Scapulae,  &,)  .  .  2 

Arm  bones,  (Ossa  humeri,  c,)  .  ^  2- 

Fore  arm  bones,  Radii  et  ulnae,  d,  e,)  .  .  4 

Wrist  bones,  (Ossa  carpi,/,)  .  .  16 

Hand  bones,  (Ossa  metacarpi,  ^,  .  .  8 

Finger  bones,  (Phalanges  digitorum  manus,  h,  i,  k,)  24 
Thumb  bones,  (Ossa  policis,  Z,)  .  .  6 

Sessamoid  bones, (Ossa  sessamoidea)  .  _4_ 

Total  68 

'6  The  inferior  extremities  contain  64  bones,  viz: 
Thigli  bones,  (Ossafemoris,  a,) 
Knee-pans,  (Patelffi,  6,) 
Shin  bones,  (Tibiae,  c,)     . 
Small  bone  of  the  legs,  (Fibulae) 
Tarsal,  (Ossa  tarsi,  e,)    . 
Metatarsal,  (Ossa  metatarsi,  /,) 
Toe  bones,  (Phalanges  digitorum  pedis,  h 
Sessamoid,  (Ossa  sessamoidea) 


ST 


68 


6* 


2 
2 

2 

2 
14 
10 

28 

Total,  64 

Grand  Total 


h  *,) 


64 
252 


66 


PHysroLOGY- 


^y 


THE    HUMAN    SKELETON.  67 

7-  The  second  plate  represents  a  back  view  of  the  male  skeleton, 
while  the  first  is  a  front  view. 

a.  The  parietal  bone 

b.  The  occipital  bone. 

c.  The  temporal  bone. 

d.  The  cheek  bone. 

e.  The  lower  jaw  bone. 

Neck  and  Trunk. 

a.  The  bones  of  the  neck. 

b.  The  bones  of  the  back. 

c.  The  bones  of  the  loina. 

d.  The  hip  bones. 
■e.  The  sacrum. 

Upper  Extremity. 

e.  The  collar  bonea. 

b.  The  blade  bone. 

c.  The  upper  bone  of  the  arnu 

d.  The  radius, 
c.  The  vJna. 

f.  The  bones  of  the  wrist. 
g.  The  bones  of  the  hands. 

h.  The  first  row  of  finger  bones. 
i.  The  second  row  of  finger  bones. 
k.  The  bones  of  the  thumb. 

Lower  Extremity, 

a.  The  thigh  bone. 

b.  The  large  bone  of  the  leg. 

c.  The  small  bone  of  the  leg, 

d.  The  heel  bone. 

c.  The  bones  of  the  instep. 
/.  The  bones  of  the  toes. 

6.  It  does  not  fall  within  the  plan  of  the  present  work  ta 
give  a  description  of  the  individual  bones  which  go  to  make 
tip  the  skeleton ;  this  must  be  sought  in  treatises  on  anatomy. 
Still  there  are  many  points  connected  with  the  subject  of  ex- 
treme interest  to  every  reflecting  mind,  to  which  the  atten- 
tion of  the  young  may  be  profitably  directed,  particularly  as 
connected  with  the  marks  of  wisdom  and  design  in  the  Al- 
mighty architect.  If  our  curiosity  is  excited  to  see  a  piece 
of  ingenious  machinery,  or  a  new  engine,  shall  we  neglect  to 
raise  the  covering  which  displays  in  the  body  the  most  strik- 
ing proofs  of  design,  surpassing  all  art  in  simplicity  and 
©fFectiveness,  and  without  any  thing  useless  or  superfluous. 


68  PHYSIOLOGY. 

9.  If  we  compare  the  human  body,  as  a  work  of  art,  with 
any  forms  of  human  architecture,  how  vastly  superior  does 
it  appear.  A  watch,  or  a  musical  automaton  are  highly  in- 
genious specimens  of  inventive  skill ;  but  where  is  the 
watch  or  the  automaton  that  can,  without  repair,  for  the 
space  of  80  or  100  years,  continue  to  perform  its  movements 
with  regularity  and  precision.  And  yet  how  much  less 
complicated  is  their  machinery,  how  vastly  more  solid,  and 
durable  the  materials  out  of  which  they  are  formed  ! 

10.  If  we  examine  a  ship,  we  find  it  built  for  passive  mo- 
tion, and  for  resisting  force  externally  applied  ;  a  house  or  a 
bridge  is  constructed  for  solidity  and  firmness,  on  the  prin- 
ciple of  gravitation ;  a  railroad  car  is  built  for  rapid  motion, 
and  its  wheels  so  adjusted,  that  they  may  not  run  off  the 
track ;  but  in  the  human  body,  we  find  not  only  securi- 
ties against  the  gravitation  of  the  parts,  provisions  to  with- 
stand shocks  and  injuries  from  without,  but  at  the  same  time^ 
the  frame  work  is  calculated  to  sustain  an  internal  impulse 
from  the  muscular  force  which  moves  the  bones  as  levers,  or 
like  a  hydraulic  engine,  propels  the  fluids  through  the  body. 

11.  The  human  fabric  is  admirably  adapted  to  resist  the 
influences  to  which  it  is  subjected  ;  in  other  words,  there  is 
a  nice  balance  between  the  power  of  exertion  and  the  capa- 
bility of  resistance.  A  deer  or  a  giraffe  is  never  injured  by 
any  leap  which  their  muscular  powers  enable  them  to  make^ 
because  the  inert  power  of  resisting  the  shock,  bears  a  rela- 
tion to  the  muscular  power  with  which  they  spring  ;  and  so 
it  is  in  man.  The  elasticity  of  his  limbs  is  proportioned  very 
accurately  to  his  activity;  he  readily  resists  shocks  and  im- 
pulses upon  the  lower  extremities,  because  they  are  adapted 
to  this  end ;  but  if  the  same  are  applied  to  the  upper,  the 
bones  are  broken  or  displaced,  because  they  are  adapted 
rather  for  extensive  and  rapid  motion,  than  for  resisting  vio- 
lent shocks. 

12.  It  has  been  truly  remarked  that  the  foundation  of  tha 
Eddystone  light-house,  the  perfection  of  human  architecture 


THE    HUMAN    SKELETON.  69 

and  ingenuity,  is  not  formed  on  principles  so  correct,  as  those 
which  have  directed  the  arrangement  of  the  bones  of  the  feet ; 
that  the  most  perfect  pillar  is  not  adjusted  with  the  accuracy 
of  the  hollow  bones  which  support  our  weight ;  that  the  in- 
sertion of  a  ship's  mast  into  the  hull  is  a  clumsy  contrivance 
compared  with  the  connexions  of  the  human  spine  and  pel- 
vis ;  and  that  the  tendons  are  composed  in  a  manner  supe- 
rior to  the  improved  chain  cables  of  Bloxham. 

13.  As  the  head  is  the  noblest  part,  and  the  brain  the 
most  essential  organ  of  the  animal  system,  let  us  first  direct 
our  attention  to  it.  The  brain  is  liable  to  injuries,  not  only 
by  sharp  bodies  touching  and  entering  it,  but  by  a  blow  upon 
the  head,  which  shall  vibrate  through  it,  without  the  instru- 
ment piercing  the  skull  ;  and  such  a  blow  would  more  effec- 
tually destroy  a  man's  senses,  than  even  if  a  sword  pene- 
trated into  its  substance.  It  is  obvious,  that  if  the  bony 
case  were  soft  it  would  be  easily  pierced  ;  if  of  a  brittle 
nature,  it  would  be  easily  cracked,  and  if  very  firm  and  solid, 
like  metal,  it  would  ring  and  vibrate,  and  thus  communicate 
the  concussion  to  the  brain. 

14.  To  obviate  these  dangers,  we  find  the  skull  composed 
of  two  plates  of  bone,  one  externa],  which  is  fibrous  and 
tough,  and  one  internal,  so  dense  and  hard,  that  it  is  called 
by  anatomists  the  glassy  table.  Now,  as  the  brain  is  liable 
to  be  hurt  both  by  sharp  and  blunt  instruments,  the  inner 
table  is  hard  and  brittle,  calculated  to  resist  any  thing  pene- 
trating ;  while  the  outer  table  is  tough  to  give  consistence, 
and  stifle  the  vibration  which  would  take  place,  if  the  whole 
texture  were  uniform.  This  may  be  illustrated  by  an  ex- 
ample. If  a  soldier's  head  be  covered  with  a  steel  helmet 
or  cap,  the  blow  of  a  sword,  which  does  not  penetrate,  will 
yet  bring  him  to  the  ground  ;  but  if  it  be  lined  with  leather 
and  covered  with  hair,  the  vibration  is  not  transmitted  to 
ihe  brain,  and  the  wearer  escapes  without  injury. 


70  PHYSIOLOGY. 


■a,  the  external,  h,  c,  the  internal  table;  the  intermediate  cellular 
texture,  being  soft  and  spongy,  and  conveying  vessels  and  nerves  from 
one  part  to  another. 

15.  It  is  worthy  of  particular  remark,  how  the  changes 
in  the  structure  of  the  bones  of  the  skull  are  adapted  to  the 
changes  in  the  mind  at  different  periods  of  life.  At  birth, 
the  skull  is  soft  and  yielding,  there  being  considerable  inter- 
vals between  the  adjacent  bones  of  which  it  is  composed  ; 
during  childhood,  it  is  highly  elastic,  so  that  the  heedlessness 
of  that  period  may  not  endanger  concussion,  to  which  it  is 
so  often  exposed  from  falls  ;  and  during  youth  and  up  to 
manhood,  the  parts  which  are  exposed  to  the  contact  of  ex- 
ternal bodies,  are  thicker,  and  the  bones  are  still  not  firmly 
consolidated  at  their  sutures  or  seams,  by  which  they  are 
united.  As  old  age  approaches,  man  grows  more  timid,  and 
is  little  disposed  to  feats  of  agility  or  activity  ;  something 
leaches  him  that  falls  or  blows,  which  could  once  be  borne 
with  impunity,  can  no  longer  be  encountered  with  safety; 
and  if  we  examine  the  skull,  we  find  the  two  layers  of  bone 
consolidated  into  one.  The  result  of  which  is,  that  con- 
cussion  at  this  period  would  be  far  more  dangerous  than  in 
early  life,  or  at  the  age  of  manhood. 

16.  The  sutures,  or  joinings  of  the  bones  of  the  skull,  in- 
terrupts, in  a  measure,  the  shock  of  the  vibration  produced 
by  external  violence,  and  also  prevent  fractures  from  extend- 
ing as  far  as  they  otherwise  would  do,  in  one  continued  bony 
substance.  No  one  can  examine  the  joinings  of  two  of  the 
bones  of  the  cranium,  without  admiring  the  minute  dove- 
tailing by  which  one  portion  of  the  bone  is  inserted  into, 
and  surrounded  by  the  other,  whilst  that  other  pushes  its 
processes  out  between  those  of  the  first  in  the  same  manner  i 


THE    HUMAN    SKELETON.  Tl 

and  the  fibres  of  the  two  bones  are  thus  interlaced,  as  you 
might  interlace  your  fingers.  But  this  dove-tailing  exists 
only  in  the  external  plate  ;  on  the  internal  surface  the  bones 
are  simply  laid  in  contact. 

17.  Sir  Charles  Bell  compares  the  human  skull  to  the 
dome  of  a  building,  which  is  acknowledged  to  be  one  of 
the  most  difficult  pieces  of  architecture.  The  dome  of  St. 
Sophia,  in  Constantinople,  built  in  the  time  of  the  Emperor 
Justinian,  fell  three  times  during  its  erection  ;  and  the  dome 
of  the  Cathedral  of  Florence,  stood  unfinished  120  years  for 
want  of  an  architect.  "  Yet,"  says  this  writer,  "  we  may, 
in  one  sense  say,  that  every  builder  who  tried  it,  as  well  as 
every  labourer  employed,  had  the  most  perfect  model  in  his 
own  head."  The  difficulty  in  constructing  a  dome,  is  the 
tendency  of  the  weight  of  its  upper  part,  to  disengage  the 
stones  from  each  other  which  form  the  low^er  circle,  and 
crowd  out  the  circular  wall  on  which  it  rests.  This  is- 
guarded  against,  either  by  soldering  the  stones  into  each 
other,  or  by  hooping  them  together  by  strong  iron  hoops. 
The  dome  of  St.  Paul's,  in  London,  is  secured  by  several 
strong  double  iron  chains,  linked  together  at  the  bottom  and 
along  the  sides  of  the  cone.  Now,  in  the  bones  which  com- 
pose the  dome  of  the  cranium,  we  find  the  edge  of  a  bone  at 
the  suture  lying  over  the  adjoining  bone  at  one  part  and 
under  it  at  another  ;  which,  w4th  the  dove-tailing  above- 
mentioned,  holds  each  bone  securely  in  its  place.  But  while 
a  dome  is  calculated  to  resist  one  kind  of  force,  viz.  that 
acting  perpendicularly,  or  in  the  direction  of  gravity,  the 
skull  is  equally  calculated  to  resist  forces  operating  in  all 
directions.  Thus  it  can  be  shown,  that  no  other  form  of 
equal  strength  could  be  devised.  AVhen  we  reflect  on  the 
strength  displayed  by  the  arched  film  of  an  egg-shell,  we 
need  not  wonder  at  the  severity  of  blows  which  the  cranium 
can  withstand. 


72 


PHYSIOLOGY. 


fl,  a,  the  coronal,  suture,  from  the  Latin  corona,  crown,  so  called 
from  its  situation  on  that  part  of  the  head,  upon  which  the  ancients 
placed  the  laurel,  or  olive  crown,  given  to  the  victors  in  their  games. 
It  connects  the  frontal  to  the  parietal  bones ;  h,  the  sagittal  suture, 
from  a  Latin  word,  signifying  arrow,  from  its  straight  course.  It  runs 
from  the  middle  of  the  frontal  to  the  angle  of  the  occipital  bone,  con- 
necting the  two  parietals ;  c,  the  lamhdoidal  suture,  extending  from 
the  sagittal  suture  down  to  the  base  of  the  brain  on  each  side  ;  e,  e, 
the  scaly  overlapping  of  the  temporal  upon  the  parietal  bones ;  hence 
called  squamous  suture, 

18.  The  frontal  bone  is  one  of  the  most  important  in  the 
skull.  It  has  been  compared  to  a  clam-shell  from  its  shape, 
and  it  forms  the  fore-head,  part  of  the  temples,  and  the  roof 
of  the  orbits  of  the  eyes.  Like  the  other  bones,  it  is  com- 
posed of  two  plates,  which  often  recede  from  each  other, 
immediately  over  the  nose  to  a  considerable  distance,  leaving 
a  space  between  them  called  the  frontal  sinuses.  These 
cavities  communicate  with  the  nose,  and  are  supposed  to 
increase  the  intensity  of  the  sound  of  the  voice,  and  also  ta 
render  it  more  melodious.  The  change  of  voice,  observable 
in  a  person  affected  with  a  cold,  is  owing  to  a  closure  of  the 
passage  between  the  nose  and  cavity,  preventing  the  access 


THE    HUMAN    SKELETON. 


73 


of  the  sound  to  this  reverberating  sinus.  SnufF-taking,  it 
has  been  supposed,  injures  the  voice  by  obstructing  this 
canal. 


A  front  view  of  the  frontal  bone  ;  «,  a,  frontal  sinuses  ;  5,  the  tenw 
poral  arch,  beneath  which  lies  the  temporal  muscle,  which  closes  the 
iower  jaw  ;  d,  the  supra-orbitary  hole  for  a  psssage  of  a  branch  of  the 
fifth  pair  of  nerves. 

19.  The  shape  of  the  head,  as  welLas  its  size,  varies  great* 
ly  in  different  individuals.  There  are  also  national  peculi- 
arities in  the  form  of  the  head,  constituting  a  well-marked 
national  feature.  Thus  the  Caucasian  race,  to  whom  we 
belong,  is  distinguished  by  the  beautiful  oval  form  of  the 
head.  To  this  race  the  most  civilized  nations  belong,  and 
those  which  have  ruled  over  the  others.  The  Mongolian 
race,  which  inhabits  China  and  Japan,  is  known  by  its 
prominent  cheek  bones,  flat  face,  narrow  and  oblique  eyes, 
straight  and  black  hair,  thin  beard,  and  olive  complexion. 

2"0.  The  negro  race  has  a  compressed  skull,  and  a  flat- 
tened nose,  a  prominent  mouth,  and  thick  lips ;  thus  bearing 
some  resemblance  in  features  to  the  monkey  tribe.  The 
North  American  Indian  has  a  very  singular  shaped  head  ; 
it  being  high  from  the  ear  upward,  and  short  from  the  front 

to  the  back.     The  fore-head  is  not  as  largely  developed  a^. 

7 


74  PHYSIOLOGT. 

in  the  Caucasian.  The  head  of  the  Hindoo  is  much  smaller 
than  that  of  the  European,  while  that  of  the  New-Hollander 
is  but  little  superior  to  that  of  the  ourang  outang,  who  roams 
the  same  forests  with  himself.  The  New  Zealanders  have 
heads  nearly  as  large  as  the  European  ;  but  the  fore-head 
is  low,  and  the  great  preponderance  of  size  is  in  the  back 
part  of  the  head. 

21.  The  heads  of  the  ancient  Egyptians,  as  appears  from 
an  examination  of  mummies,  closely  resembled  in  shape  and 
size  those  of  modern  Europeans.  Some  of  our  North  American 
Indians  are  in  the  habit  of  flattening  their  heads  by  binding 
a  piece  of  board  on  the  fore  as  well  as  back  part  of  the  head, 
in  infancy.  From  this  custom,  one  tribe  among  the  Rocky 
Mountains,  has  received  the  name  of  Flat  Head  Indians. 
The  Choctaw  tribe  were  formerly  in  the  habit  of  flattening- 
their  heads  in  the  same  way  ;  but  for  some  years  past,  they 
have  discontinued  the  practice.  The  heads  of  the  different 
European  nations  differ  somewhat  from  each  other ;  but  a 
common  type  characterizes  them  all. 

22.  Not  only  the  size,  but  the  texture  of  skulls  among  dif- 
ferent nations  varies.  The  grain  of  the  New  Holland  skulls 
is  extremely  rough  and  coarse ;  that  of  the  Hindoos,  fine, 
smooth,  and  compact,  more  closely  resembling  ivory.  The 
Swiss  skulls  are  open  and  soft  in  the  grain,  while  the  Greek 
are  closer,  and  finer.  It  has  been  suggested  that  there  may 
possibly  be  a  corresponding  quality  of  brain  in  the  individu- 
als, which  may  influence  the  mental,  and  consequently  the 
national  character.  This  difference  is  generally  attributed 
to  the  effects  of  temperament. 

23.  The  bones  of  the  cranium  increase  in  extent,  thick- 
ness, and  weight,  from  the  commencement  till  the  termina- 
tion of  their  development  in  adult  age  \  but  after  this  time, 
and  till  old  age,  they  always  diminish  in  these  three  rela- 
tions. In  advanced  life,  we  often  find  them  reduced  to  a 
mere  shell,  and  perhaps  perforated  in  some  places.  They 
thus  become  much  lighter  than  in  middle  life.    Meckel  found 


THE    HUMAN    SKELETON.  75 

the  skull  of  a  female,  seventy  years  of  age,  weigh  but  four- 
teen ounces,  while  that  of  a  girl,  twenty  years  of  age, 
weighed  twenty-four  ounces.  In  the  early  periods  of  life, 
the  whole  form  of  the  head  is  much  rounder  than  at  an 
advanced  age  ;  owing,  perhaps,  to  the  small  development  of 
the  face,  which  the  skull  envelopes  in  every  direction. 

24.  The  size  of  the  cavity  formed  by  the  bones  of  the 
skull,  is  always  proportional  to  the  size  of  the  organs  it 
lodges  and  protects.  The  shape  and  size  of  the  cranium  de- 
pend on  the  brain,  and  not  of  the  brain  on  the  cranium.  The 
soft  parts  model  and  adapt  to  themselves  the  hard,  and  not 
■the  hard,  the  soft.  The  brain  is  formed  before  the  case 
which  contains  it,  and  it  is  not  till  after  several  years  that 
.the  bones  of  the  cranium  become  perfectly  consolidated.  In 
a  child  of  ten  years  of  age,  afflicted  with  dropsy  in  the  head 
from  infancy,  and  which  was  exhibited  a  year  or  two  since 
in  this  city  as  a  great  curiosity,  although  the  head  measured 
thirty-two  inches  in  circumference  above  the  ears,  yet  nearly 
the  whole  surface  was  protected  by  a  bony  covering. 

25  The  Spine. — However  admirably  the  skull  may 
appear  to  be  adapted  to  the  objects  for  which  it  was  obviously 
designed,  the  spine  exhibits  no  less  evidence  of  wisdom  and 
skill  in  the  divine  Architect.  In  addition  to  the  firmness 
which  was  required  in  the  joinings  of  the  bones  of  the  cra- 
nium, a  new  principle  is  now  introduced,  viz.  the  attainment 
of  mobility  or  pliancy.  The  spinal  column  indeed  serves 
three  important  purposes  ;  it  is  the  great  bond  of  union  be- 
tween all  the  parts  of  the  skeleton  ;  it  forms  a  tube  for  the 
safe  lodgment  of  the  spinal  marrow  ;  and  lastly,  it  is  a  pillar 
to  sustain  the  head, 

26.  In  order  to  accomplish  these  various  purposes,  the 
back  bone,  so  called,  is  composed  of  twenty-four  distinct 
bones,  or  vertehrcB,  from  vertere,  to  turn,  as  the  body  turns  on 
them,  which  are  arranged  into  three  classes,  the  cervical, 
dorsal,  and  lumbar.  The  first  seven  are  the  cervical,  because 
they  belong  to  the  neck ;  the  next  twelve  are  the  dorsal,  be- 


76 


PHYSIOLOGY. 


cause  they  belong  to  the  back ;  and  the  last  five  are  the 
lumbar,  because  they  are  situated  in  the  loins.  The  bones 
comprising  these  classes,  differ  somewhat  from  each  other  in 
shape ;  a  description  of  the  dorsal  pieces  will  prove  sufficient 
for  our  purpose. 


A  lateral  view  of  the  spine  divided  into  its  cervical,  dorsal,  and  lum, 
bar  portions. 


27.  Each  of  these  twelve  bones  consists  of  a  body,  four 
articulating  processes,  two  transverse  processes,  and  one  spi- 
nous process.  The  body  is  formed  of  soft  and  spongy  bone, 
which  is  circular  before,  flat  towards  the  sides,  hollowed  out 
behind  into  a  crescent  shape  for  containing  the  spinal  mar- 
row, and  concave  above  and  below  for  the  accommodation 
of  the  intervertebral  substance.     On  the  side  of  the  bone  are 


THE    HUMAN    SKELETON.  77 

situated  the  four  articulating  processes^  each  bone  being  con- 
nected with  the  two  immediately  adjoining  it.  Two  of  these 
processes  are  situated  near  its  upper  surface  to  articulate 
with  corresponding  processes  belonging  to  the  bone  above, 
and  two  are  placed  near  its  under  surface  to  join  with  those 
of  the  bone  below.  The  two  superior  articulating  processes 
of  one  vertebrae  are  thus  connected  with  the  two  inferior 
articulating  processes  of  another,  and  these  points  of  union 
not  only  co-operate  with  the  intervertebral  cartilages  in 
keeping  these  two  vertebrae  together,  but  permit  a  slight 
rotatory  motion  of  the  one  upon  the  other.  The  spinous 
process  projects  directly  backwards  from  the  body  of  the  ver- 
tebrae, and  may  be  felt  externally  by  passing  the  hand  along 
the  spine ;  the  two  transverse  stand  out  on  either  side,  and 
have  the  ends  of  the  ribs  attached  to  them. 


A  vertebra  of  the  neck  ;  a,  body  of  the  bone.;  h,  the  spinal  process; 
c,  d,  the  transverse  processes  double,  showing  circular  holes  for  the 
passage  of  the  vertebral  artery ;  e,  e.  the  superior  ;  /,  /,  the  articular, 
or  oblique  processes ;  g,  the  spinal  hole  for  the  spinal  marrow.  The 
roots  of  the  articular  processes  are  hollowed  out  above  and  below 
into  notches ;  and  these,  when  the  bones  are  fitted  together,  form  aper- 
tures on  each  side  of  the  spine,  through  which  the  nerves  pass  out  from 
the  spinal  canal. 


78 


PHYSIOLOGY. 


A  vertebra  of  the  loins  ;  a,  a,  their  bodies,  larger  and  more  spongy 
than  those  of  the  others ;  b,  b,  b,  the  superior  ;  c,  c,  c,  the  inferior  ar- 
ticular processes,  strong  and  deep,  the  superior  concave  ;  the  inferior 
convex ;  d,  d,  d,  the  transverse  processes,  small  and  long,  serving  as 
levers  for  the  attachment  of  muscles  ;  e,  e,  the  spinous  processes, 
strong,  horizontal,  and  flattened  at  the  sides ;  /,  the  spinal  faramen. 

28.  The  vertebrae,  as  I  have  stated,  are  not  in  contact, 
but  separated  by  a  considerable  interval,  which  is  filled  by  a 
peculiar  gristly  substance  of  a  highly  elastic  nature,  which 
is  pressed  out  from  betwixt  the  bones,  and  therefore  permits 
them  to  approach,  and  play  a  little  in  the  motions  of  the 
body.  This  compressible  cushion  of  cartilage  and  ligament 
serves  indeed  the  triple  purpose  of  uniting  the  bones  to  each 
other,  of  diminishing  and  diffusing  the  shock  in  walking  or 
leaping,  and  of  admitting  a  greater  extent  of  motion  than  if 
the  bones  were  in  more  immediate  contact.  These  separate 
vertebrae  are  firmly  bound  to  each  other  in  such  a  way  as  to 


THE    HUMAN    SKELETON.  79 

admit  of  flexion  and  extension,  and  a  certain  degree  of  rota- 
tion, while  by  their  soUdity  and  firm  attachment  to  each 
other,  great  strength  is  secured. 

29.  We  can  now  readily  perceive  how  great  the  influence 
of  these  twenty-four  joinings  must  be  in  giving  elasticity  to 
the  whole  column,  and  how  much  this  must  tend  to  the  pro- 
tection  of  th€  brain.  Indeed,  were  it  not  for  the  interposi- 
tion of  this  elastic  material,  every  motion  of  the  body  would 
produce  a  jar  to  the  delicate  texture  of  the  brain,  and  we 
should  suffer  almost  as  much  in  alighting  on  our  feet,  as  in 
falling  on  our  head. 

30.  But  there  is  another  very  curious  provision  for  the 
protection  of  the  brain,  and  that  is  the  curved  form  of  the 
spine.  By  looking  at  the  cut,  you  see  that  it  is  shaped  like 
an  italic/.  Now,  suppose  it  were  straight,  and  stood  per- 
pendicularly, it  is  evident  that  when  we  ahghted  on  our  feet 
it  would  recoil  with  a  sudden  jerk,  like  a  straight  steel 
spring  pressed  between  the  hands,  from  its  extremities.  In 
such  a  case,  the  weight  bearing  equally,  the  spine  would 
neither  yield  to  one  side  or  the  other,  and  consequently,  there 
would  be  a  resistance,  from  the  pressure  on  all  sides  being 
balanced.  But  shaped  as  it  is,  we  find  it  constantly  yielding 
in  the  direction  of  its  curves  ;  the  pressure  is  of  necessity 
more  on  one  side  of  the  column  than  on  the  other,  and  its 
elasticity  is  immediately  in  operation  without  a  jerk.  It 
yields,  recoils,  and  so  forms  the  most  perfect  spring,  admirably 
calculated  to  carry  the  head  without  jar  or  injury  of  any 
kind. 

31.  When  we  reflect  that  the  spinal  column  is  composed 
of  so  many  separate  parts,  so  nicely  adapted  to  each  othei', 
and  kept  in  place  by  such  a  complicated  array  of  ligaments, 
tendons,  and  muscles,  we  might  expect  that  injuries  and  dis- 
eases of  the  structure  would  be  very  frequent.  But  fortu- 
nately this  is  not  the  case,  except  where  undue  restraint  and 
confinement  are  imposed  ;  and  it  is  only  within  a  fe^Y  years 


so  PHYSIOLOGY. 

since  a  change  has  been  introduced  into  the  system  of  edu- 
cation for  young  ladies,  that  the  spine  disease,  so  called,  has 
become  a  common  affection. 

32.  Every  one  who  has  paid  the  least  attention  to  physi- 
ology, is  aware  that  a  certain  degree  of  exercise  is  as  neces- 
sary to  the  growth  and  strength  of  the  body,  and  of  every 
part  of  it,  as  nourishment  itself;  and  that  if  such  exercise 
be  withheld  during  the  period  of  growth,  the  body  never  ac- 
quires its  due  form  and  proportions,  and  often  is  permanently 
crippled.  How  cruel  it  is,  then,  to  repress  that  overflow  of 
life  and  energy,  which  nature  has  given  to  young  creatures, 
to  prompt  them  to  that  exertion  which  is  necessary  to  the 
full  development  of  their  physical  powers  ;  and  instead  of 
-allowing  the  young  of  both  sexes  to  jump,  and  skip,  and 
dance,  and  play,  as  nature  dictates,  to  curb  all  propensity 
to  such  vulgar  activity,  for  fear  that  they  may  not  receive 
the  praise  of  being  well-bred.  How  preposterous,  unnatural, 
4ind  ruinous  is  the  practice  of  confining  delicate  females  for 
hours  together  every  day  to  sedentary  employment,  the  sure 
consequence  of  which  will  be,  weakness  of  the  body  generally, 
and  of  the  back  in  particular,  especially  if  the  seat  be  a  stool 
which  has  no  back,  or  even  a  narrow  chair  with  a  perpen- 
<3icular  back. 

33.  The  effect  of  such  a  practice  is,  that  in  consequence 
of  the  fatigue  induced  b^^  such  a  posture,  the  spine  gives  way 
in  some  part  and  bends,  and  in  a  little  time  the  curvature 
becomes  permanent.  And  often  when  a  bend  has  taken 
place  in  one  direction,  there  immediately  follows  an  opposite 
bend  above  or  below,  to  keep  the  centre  of  gravity  of  the 
body  always  directly  over  the  base ;  the  curve  accordingly 
thus  becomes  double,  like  an  italic  /,  and  the  distortion  is 
rendered  complete. 

34.  The  means  employed  to  remedy  this  affection  almost 
invariably  make  it  worse.  In  the  first  place,  strong,  stiff 
stays  are  put  on,  to  support  the  back,  as  it  is  said  ;  and  so 
they  do,  perhaps,  while  they  are  on  j  but  as  they  supersede 


THE    HUMAN    SKELETON.  81 

the  action  of  the  muscles,  placed  there  by  nature  as  the  sup- 
ports, they  cause  these  to  lose  their  strength  ;  and  when  the 
stays  are  withdrawn,  the  muscles  are  found  too  weak  to  sup. 
port  the  body.  Other  mechanical  expedients  may  now  be 
employed,  the  back  may  be  forcibly  stretched  by  pullies,  or 
the  patient  may  be  kept  all  day  and  night  lying  on  an  inclin- 
ed plane.  The  victim  of  fashion  may  next,  perhaps,  be 
placed  under  the  charge  of  a  regular  spine  doctor,  who,  by 
means  of  pulleys,  screws,  paddings,  stays,  and  close  confine- 
ment, destroys  what  little  chance  there  still  remains  of  a 
cure.  A  decline  now  sets  in,  and  the  sufferer  sinks  into  an 
early  grave. 

35.  Dr.  Arnott  justly  remarks, — "  it  would  be  accounted 
madness  to  attempt  to  improve  the  strength  and  shape  of  a 
young  race  horse  or  grey  hound,  by  binding  tight  splints  or 
stays  round  its  beautiful  young  body,  and  then  tying  it  up 
in  a  stall ;  but  this  is  the  kind  of  absurdity  and  cruelty 
which  has  been  so  commonly  practised  in  this  country  to- 
wards what  may  well  be  called  the  most  faultless  of  created 
beings."  This  disease  may  always  be  prevented  by  suitable 
exercise,  and  the  same  remedy  so  applied,  as  directly  to 
strengthen  the  affected  part,  will  hold  out  the  best  prospect 
of  a  cure.  Boys  never  suffer  from  the  spine  disease,  because 
steel  and  whalebone  in  them  are  never  made  to  perform  the 
office  which  God  designed  for  the  bones  and  muscles. 

36.  The  Chest. — The  thorax,  or  chest  extends  above  from 
the  first  bone  of  the  neck,  by  which  it  is  connected  with  the 
head,  to  the  diaphragm  below,  by  which  it  is  divided  from 
the  abdomen.  It  is  composed  of  bones,  muscles,  and  car- 
tilages,  so  disposed  as  to  sustain  and  protect  the  most  vital 
parts,  the  heart  and  lungs,  and  to  turn  and  twist  with  perfect 
facility  in  every  motion  of  the  body,  and  to  be  constantly  in 
motion  in  the  act  of  respiration,  without  the  least  cessation 
during  a  whole  life.  In  front,  the  chest  is  bounded  by  the 
sternum,  or  breast-bone  ;  behind  by  the  spinal  column,  or 
back-bone,   and   at   the    sides   by   the   ribs.      Below,    th© 


82  PHYSIOLOGY. 

diaphragm  forms  a  membranous  partition  between  it  and 
the  cavity  of  the  abdomen.  It  is  conical  in  shape,  Vvdth  its 
apex  above,  where,  indeed,  it  is  so  contracted,  that  there  is 
barely  room  in  the  aperture  to  contain  the  tubes  which  go 
to  the  lungs  and  stomach,  and  for  the  larger  blood-vessels 
that  go  and  come  from  the  heart. 


Thorax  or  chest ',  «,  the  sternum  j  h,  6,  the  spinej  c,  e,  the  ribs,  the 
cartilages  bemg  in  front. 

37.  The  ribs  are  24  in  number,  twelve  on  each  side,  of 
which  the  seven  upper  are  united  to  the  sternum  by  car- 
tilage, and  are  called  true  ribs ;  the  cartilages  of  the  other 
five  are  united  with  each  other,  and  are  not  attached  to  the 
sternum  ;  these  are  called  false  ribs ;  all  of  them  are  con- 
nected behind  to  the  spinal  column.  The  ribs  increase  in 
length  as  far  as  the  seventh,  by  which  the  cavity  of  the 
chest  is  enlarged  ;  from  the  seventh,  they  successively  dimin- 
ish in  lengthy  thus  diminishing  the  cavity.     The  direction 


THE    HUMAN    SKELETON. 


83P 


of  the  ribs  from  above  downwards  is  oblique,  forming,  as  it 
were,  a  bundle  of  hoops  playing  on  each  other. 

38.  The  curve  of  the  ribs  diminishes  considerably  from 
the  first  to  the  twelfth  ;  the  second,  however,  is  usually  more 
curved  than  the  first.  The  inferior  ribs  are  very  flat ;  the 
twelfth  is  sometimes  straight.  The  external  surface  of  each 
rib  is  convex,  the  internal  concave.  Each  rib  on  its  outer 
surface  near  the  spine  presents  an  oblique  ridge,  occasioned 
by  the  insertion  of  a  muscle  ;  and  at  this  point  there  is  a 
curvature  somewhat  abrupt,  called  the  angle  of  the  rib. 


Fourth  rib ;  a,  vertebral  extremity,  called  the  head,  which  is  connect, 
ed  with  the  bodies  of  the  two  contiguous  dorsal  vertebrae.  At  h,  the 
bone  is  contracted,  forming  the  neck  \  c,  is  the  tubercle  at  the  back  of 
the  rib,  which  is  articulated  with  the  transverse  process  of  the  ver- 
tebrae ;  d,  the  angle  ;  c,  the  sternal  extremity  ;  /,  a  groove  for  the  inter- 
costal vessels.     This  will  serve  for  a  general  description  of  the  ribs. 


Twelfth  rib,  nearly  straight. 

89.  Sternum. — Between  the  forward  ends  of  the  ribs, 
directly  in  front  of  the  chest,  lies  the  sternum^  or  breast- 
bone. It  is  light  and  spongy,  depending  chiefly  for  its 
strength  on  the  numerous  ligaments  which  cover  it.  In  the 
child,  it  is  divided  into  eight  pieces  by  cartilaginous  portions. 


84 


PHYSIOLOGY. 


which  as  life  advances,  are  reduced  to  three  ;  and,  in  old 
age,  are  united  into  one.  It  terminates  below  in  a  sharp- 
pointed  cartilage,  which  lies  over  the  stomach,  and  may  be 
felt  externally.  It  is  somewhat  hollowed  beneath  at  its 
upper  end  "for  the  passage  of  the  treachea  or  wind-pipe, 
which  lies  directly  under  it  ;  and  on  each  side  there  are 
seven  oval  depressions  for  admitting  the  cartilaginous  ex* 
tremities  of  the  first  seven  ribs. 


40.  The  sternum  in  this  cut  consists  of  two  bones.  The 
first  is  broad  and  thick  above,  and  contracts  as  it  descends. 
It  is  convex  before  and  concave  behind.  At  the  upper  angle 
a,  the  collar-bone  is  articulated  ;  h,  the  articular  surface  for 
the  cartilage  of  the  first  rib  ;  b,  for  second  rib  ;  c,  d,  e,  f,  g, 
mark  the  articular  surfaces  of  the  3d,  4th,  5th,  6th,  and  7th 
ribs  ;  h,  the  ensiform  cartilage^  terminates  the  lower  extrenv- 


THE    HUMAN    SKELETON.  86 

ity  of  the  sternum.     In  old  people,  this  cartilage  is  often 
changed  into  bone. 

41.  The  manner  in  which  the  ribs  are  attached  to  the 
sternum  by  means  of  slips  of  elastic  cartilage,  is  worthy  of 
particular  notice.  It  is  to  this  circumstance  that  it  is 
owing,  that  the  ribs  are  so  seldom  injured  by  blows  and  falls  ; 
for  if  they  were  wholly  bone  from  one  extremity  to  the  other, 
life  would  be  endangered  by  any  accidental  fracture,  and 
even  the  rubs  and  jolts  to  which  we  are  continually  exposed, 
would  be  too  much  for  their  delicate  and  brittle  texture. 
When  we  lean  forward  or  to  one  side,  the  ribs  accommodate 
themselves  not  by  a  change  of  form  in  the  bones,  but  by  the 
benditig  of  the  cartilages.  It  is  owing  to  this  elasticity  that 
the  blows  of  boxers  so  seldom  succeed  in  fracturing  the  ribs ; 
as  they  yield  in  proportion  to  the  violence  of  the  force  in- 
flicted. But  this  is  not  the  case  in  old  age.  Then  the  car- 
tilages of  the  ribs  become  bony,  and  the  whole  arch  unyield- 
ing and  inelastic  ;  so  that  blows  which  formerly  would  have 
caused  little  or  no  injury,  are  now  attended  with  fracture  of 
the  rib.  The  influence  of  the  elastic  structure  of  the  ribs,. 
in  the  action  of  breathing,  is  highly  interesting  and  import- 
ant, and  will  be  fully  explained  when  we  come,  to  treat  of 
Respiration. 

42.  The  next  division  of  the  trunk  is  called-  the  pelvis  or 
hasirif  which  consists  of  a  circle  of  large  firm  bones,  situated 
between  the  lower  portion  of  the  trunk  and  the  inferior 
extremities.  They  are  the  sacrum,  the  coccyx,  the  ilium,  the 
ischium,  and  the  pubis.  The  ilium  forms  the  upper,  the 
ischium-  the  lower,  while  the  pubis  is  situated  at  the  fore  part 
of  the  pelvis  ;  and  each  one  of  these  bones  contributes  to 
form  the  large  and  deep  socket,  for  the  head  of  the  thigh 
bon«.  The  pelvis  not  only  affords  lodgment  for  the  organs 
contained  within  its  cavity,  but  it  also  sustains  the  entire 
weight  of  the  body,  and  furnishes  sockets  for  the  heads  of  the 
thigh  bones  to  roll  in,  and  a  broad  surface  for  numerous  mus- 
cles to  spring  from. 

8 


86 


PHYSIOLOGY. 


The  pelvis. 

43".  The  last  division  of  the  body  comprehends  the  upper 
and  lower  extremities.  The  upper  consist  of  the  shoulder, - 
arm,  fore-arm,  and  hand.  The  bones  composing  the  shoulder 
are  two,  the  clavicle,  or  collar  bene,  and  the  scapula,  or  the 
hlade  hone.  The  clavicle,  named  from  its  resemblance  to  a 
key,  resembles  the  italic  s,  and  extends  across  the  upper  part 
of  the  chest,  from  the  shoulder  to  the  breast  bone,  and  it 
serves  not  only  to  sustain  the  upper  extremity  and  connect 
it  with  the  chest,  but  also  to  prevent  its  falling  forward  upon 
the  thorax,  and  to  afibrd  a  fixed  point  for  steadying  the  arm 
in  the  performance  of  its  various  actions. 

44.  The  scapula,  or  shoulder  blade,  is  a  large,  flat,  trian- 
gular bone  placed  upon  the  upper  and  back  part  of  the  chest, 
and  extends  from  the  second  to  the  seventh  ribs.  It  lies  em- 
bedded in  muscleSj  and  ha&  na  connection  with  any  other 
bone  except  the  clavicle  at  a  single  point.  It  is  separated 
from  the  thorax  by  a  double  layer  of  muscles,  on  which  it  is 
placed  as  on  a  cushion;  It  serves  for  the  attachment  of  six- 
teen muscles  which  go  to  the  ribs,  the  bone  of  the  tongue^ 
the  arm,  the  head,  and  the  spine.  It  thus  serves  not  only  as 
a  support,  but  a  fulcrum  for  every  action  of  the  superior 
extremity. 


THE    HUMAN    SKELETON. 


87 


Scapula,  a,  superior  angle  ;  d,  the  glenoid  cavity,  or  socket  for  the 
round  head  of  the  arm  bone  ;  m,  the  aeromion  process  :  n,  the  coracoid 
process,  which  serve  to  protect  the  joint ;  /,  the  hase  ;  g,  the  costa,  or 
inferior  border,  and  k,  the  superior  border  of  the  triangle  ;  Z,  the  spine  • 
o,  the  semi-lunar  notch,  for  the  passage  of  an  artery,  vein,  and  nerve. 


45.  As  a  general  rule,  in  the  joints,  strength  and  security 
are  sacrificed,  in  some  degree,  to  obtain  great  freedom  and 
latitude  of  motion.  Accordingly,  we  find  that  the  shoulder 
joint,  which  allows  of  more  extensive  motion  than  any  other* 
is  also  more  frequently  dislocated.  In  the  hinge  joints,  such 
as  the  knee  and  ankle,  such  an  accident  is  comparatively 
rare.  Where  a  bone  is  dislocated,  a  regularly  educated  sur- 
geon shoirld,  if  possible,  always  be  employed  to  reduce  it,  as 
there  is  great  danger  in  trusting  to  a  natural  bone-setter,  so 
called,  who  is  entirely  ignorant  of  the  anatomy  of  the  parts. 

46.  The  OS  humeri,  or  arm  bone,  is  of  a  cylindrical  shape, 
and  forms  at  the  elbow  a  perfect  hinge-joint  with  the  two 


88  PHYSI0L0O¥. 

bones  of  the  fore-arm,  called  radius  and  ulna.  This  bone  is 
susceptible  of  all  kinds  of  motion,  elevation,  depression,  ad- 
vancing, retreating,  circumlocution,  and  rotation.  Its  scap- 
ular extremity  is  lodged  in  a  strong  membraneous  bag,  called 
the  capsular  ligament,  and  when  the  arm  is  raised  up,  the 
bone  slides  downward  in  the  glenoid  cavity,  and  thus  distends 
the  lower  part  of  the  capsular  ligament.  In  every  motion  of 
the  arm,  except  in  carrying  it  backwards,  the  scapular 
readily  moves  or  follows  it ;  it  is  therefore  during  motions  of 
the  latter  kind,  that  dislocations  of  the  joint  are  most  apt  to 
occur.  If,  therefore,  the  scapula  could  always  follow  the 
motions  of  the  arm,  it  would  rarely  be  forced  out  of  its 
socket,  and  then  only  by  extreme  violence. 

47.  In  the  fore-arm  we  find  two  kinds  of  motion,  one  at 
the  elbow,  backward  and  forward,  and  also  a  rotary  motion,  by 
which  the  palm  is  turned  upward  or  downward,  as  occasion 
requires.  These  motions  are  called  supination  and  pronation. 
Flexion  and  extension  of  the  arm  are  performed  by  means  of 
the  ulna^  which  being  articulated,  with  the  os  humeri,  by  a 
liinge  joint,  carries  the  radius  along  with  it  in  all  its  move- 
.ments.  Now  while  the  larger  part  of  the  ulna  is  above,  the 
larger  part  of  the  radius  is  below,  so  that  while  the  former 
presents  a  large  surface  for  articulation  at  the  elbow,  the  lat- 
ter does  the  same  at  the  wrist,  and  this  inverse  arrangement 
also  contributes  to  the  uniform  diameter  of  the  fore-arm. 
While  the  fore-arm  is  thus  attached  to  the  os  humeri,  the 
radius  is  attached  to  the  wrist;  so  that  when  we  turn  the 
palm  of  the  hand,  the  radius  rolls  on  the  ulna  carrying  the 
hand  with  it.  Indeed  so  admirable  is  this  contrivance,  that 
both  motions  may  be  performed  at  the  same  time,  for  while 
we  are  bending  the  arm,  we  may  also  be  rotating  or  turning 
it  upon  its  axis.  To  facilitate  these  motions,  it  will  be 
observed  that  near  the  elbow,  a  tubercle  of  the  radius  plays 
into  a  socket  of  the  ulna,  whilst  near  the  wrist,  the  radius 
finds  the  socket,  and  the  ulna  the  tubercle. 


THE    HUMAN    SKELETON. 


89 


g,  the  ulna  ;  a,  the  radiusf. 


48.  It  has  been  remarked  that  the  ulna  has  a  hooked  pro- 
-eess,  the  oZecrcfwon,  e,  which  catches  round  the  lower  end  of  the 
humerus,  forming  with  it  a  hinge  joint.  The  radius  also,  has 
a  neat,  small,  round  head,  h,  bound  to  the  ulna  by  ligaments, 
which,  as  it  turns,  carries  the  hand,  which  is  attached  to  its 
lower  extremity  along  with  it.  Now  in  animals  that  have 
solid  hoofs,  such  a  motion  woiiid  be  useless  and  a  source  of 
weakness,  accordingly  we  find  these  bones  united  together 
and  consolidated  in  such  animals.  By  an  examination  of 
these  bones  alone,  the  anatomist  is  able  to  determine  whether 
the  animal  to  which  they  belonged,  perhaps  thousands  of 
years  ago,  was  carniverous  or  graminivorous,  that  is, 
whether  he  was  an  animal  or  a  vegetable  feeder  ;  whether  he 
had  claws  or  hoofs.  If  he  finds  merely  the  end  of  the  radius, 
and  notices  in  it  a  smooth  depression  where  it  bears  against 
the  humerus,  and  the  smooth  surface  that  turns  on  the  cavity 
of  the  ulna,  he  concludes  at  once,  that  the  animal  had  a  paw, 
and  a  motion  of  the  wrist  which  implies  claws.  It  was  in 
this  way  that  Cuvier  and  Buckland  made  those  singular  and 
interesting  discoveries  in  relation  to  antediluvian  fossil 
bones,  which  have  given  such  importance  to  geological 
:i'esearches. 

49.  But  let  us  examine  this  point  a  little  further<.     If  the 

^* 


90  PHYSIOLOGY. 

examination  of  a  single  bone,  or  even  the  end  of  a  bone,  like 
that  of  the  radius,  shows  that  the  animal  to  which  it  belonged 
wa&  carniverous,  like  the  tiger,  lion  or  leopard,  it  also  shows 
the  form  of  all  the  other  bones  ;  not  only  that  the  animal  had 
teeth  to  rend  his  prey,  and  claws  to  hold  it,  but  a  spinal  col- 
umn to  admit  of  such  motion,  such  writhing  and  turning  as 
is  necessary  to  secure  it,  and  such  a  stomach  and  intestines 
as  are  adapted  to  digest  it,  in  short,  such  as  belong  to  the 
carrriver-ous  class.  How  beautiful  is  that  process  of  reason- 
ing, and  how  interesting  that  science  which  enables  us  from 
a  small  portion  of  a  skeleton,  to  determine  the  existence  of  a 
carniverous  animal,  of  a  fowl,  or  a  bat,  a  lizard,  or  a  fish; 
which  teach  us  the  wisdom  and  the  extent  of  that  plan,  which 
adapts  the  members  of  every  creature  to  its  proper  office  ; 
which  exhibits  a  system  extending  through  the  whole  range 
of  animated  beings,  whose  motions  are  conducted  -by  the  ope- 
ration of  muscles  and  bones. 

50.  Twenty-nine  bones  enter  inio  the  composition  of  the 
"human  hand,  of  which  eight  constitute  the  wrist.  The  n^ta- 
carpal  bones  support  the  fingers,  and  are  four  in.  number,  the 
thumb  being  directly  articulated  with  the  wrist.  From  this 
arrangement  there  results  great  strength,  mobility,  and  elas- 
ticity. Indeed,  it  may  be  said,  that  on  the  length,  strength, 
free  lateral  motion,  and  perfect  mobility  of  the  thumb,  de- 
pends the  power  of  the  human  hand.  In  strength  it  is  said 
:to  be  equal  to  that  of  all  the  fingers,  hence  it  is  called  pollex,. 
from  '^pollere,^^  to  have  much  strength.  If  we  examine  the 
thumb  of  the  monkey,  we  find  that  it  extends  no  farther  than 
to  the  root  of  the  fingers.  The  fingers  would  be  compara- 
tively of  little  use,,  were  it  not  for  the  fleshy  bed  of  the, 
thumb. 


THE    HUMAN    SKELETON.  91 


''Bones  of  the  hand. 

"51.  The  bones  of  the  lower  extremity  consist  of  the  thigh, 
leg  and  foot.  The  thigh  bone  (os  femoris,)  is  the  longest 
bone  of  the  human  skeleton,  and  is  remarkable  for  its  great 
strength,  supporting,  as  it  does,  the  whole  body,  and  often 
several  hundred  pounds  in  addition.  The  kip  joint  is  a  perfect 
specimen  of  the  ball  and  socket  joint.  This  is  for  the  pur- 
pose of  giving  great  extent  and  variety  of  motion  to  the 'legs, 
as  in  walking.  The  end  of  the  hip  bone  is  perfectly  round 
like  a  ball,  and  covered  with  a  smooth,  shining  cartilage  ; 
and  this  is  received  into  a  deep  cup,  also  lined  with  cartilage 
and  moistened  with  the  synovial  fluid.  Besides  all  this, 
there  are  strong  ligaments  all  around,  binding  the  bone 
firrrily  in  its  place,  so  that  it  is  a  very  rare  thing  for  it  to  be 
dislocated. 

"*"  52.  The  A;?2ee  is  a  hinge  joint  of  singular  construction.  The 
nibbing  parts  are  flat  and  shallow,  and  therefore  would 
easily  get  out  of  place,  were  it  not  for  the  very  strong  llga- 
ments  which  surround  it.  When  the  ligaments  on  the  inside 
of  the  joint  are  too  weak,  a  person  is  said  to  be  hiock-hneed, 
because  the  knees  knock  together.  In  weakly  children,  this 
deformity  may  frequently  be  cured  by  exercise.  It  can  also 
be  shown  that,  owing  to  the  air  being  completely  shut  out  of 
the  joint,  forming  what  is  called  a  vacuum,  the  bones  of  the 
knee  are  held  together  by  a  constant  pressure  of  the  atmos- 
phere equal  to  sixty  or  seventy  pounds.     On  the  fore-part  of 


92  PHYSIOLOGY. 

the  knee,  is  a  movable  bone  of  a  flat,  round  shape,  called  'pa- 
tella, or  knee-pan,  over  which  a  cord  or  tendon  passes,  which 
is  made  by  a  contraction  of  all  the  muscles  on  the  fore  part 
of  the  thigh.  This  serves  as  a  'pulley,  and  enables  the  mus- 
cles to  act  to  greater  advantage,  by  increasing  the  distance 
of  the  rope  from  the  centre  of  motion, 

53.  The  leg  below  the  knee,  is  composed  of  two  bones, 
tibia  and  fibula,  of  a  three-cornered  or  angular  shape, 
like  these  of  the  fore-arm  ;  and  the  design  no  doubt  is,  to 
form  a  pillar  of  greater  strength  than  one  bone  would 
make ;  and.  also  to  furnish  a  greater  surface  for  the  origin 
and  attachment  of  the  numerous  muscles  required  for  the 
feet.  The  ankle,  like  the  wrist,  the  elbow,  and  the  knee,  is 
a  perfect  hinge  of  great  strength.  In  front  of  it  there  is  a 
narrow  strap,  or  ligament,  which  binds  down  the  cords 
which  go  to  move  the  toes.  There  is  a  small  groove  just 
within  the  inner  ankle,  for  the  passage  of  a  tendon,  exactly 
like  a  little  pulley.  The  heel  is  a  lever  for  those  strong  mus- 
cles to  act  by,  which  form  the  calf  of  the  leg.  It  is  the  ac- 
tion of  these  muscles,,  pulling  on  the  heel,  that  lifts  the  body, 
in  walking,  dancing,  standing  on  the  toes,  dz;c.  In  the  negro, 
the  heel  is  longer  than  in  any  other  race  of  mankind. 

-54.  The  bones  of  the  foot  are  divided  into  the  tarsus, 
which  is  composed  of  seven  bones,  reaching  from  the  heel 
to  the  middle  of  the  foot.  The  metatarsus  consists  of  five 
long  bones,  parallel  to  each  other,  which  extend  from  the 
tarsus  to  the  roots  of  the  toes.  The  bones  of  the  toes  are 
called  phalanges,  from  being  itt  the  form  of  a  phalanx* 
There  are  in  all  thirty-six  bones  in  the  foot,  and  as  each 
bone  forms  a  joint,  and  as  each  joint  not  only  permits 
motion,  but  bestows  elasticity,  the  obvious  design  of  this 
number  is  to  render  the  foot  elastic,  and  thus  save  the  body 
fi'om  shocks.  It  should  be  recollected  that  each  bone  is 
tipped  with  cartilage,  that  the  fibres  composing  cartilage 
are  disposed  longitudinally  or  perpendicularly  to  the  surface 
sof  tlie  bone  and  the  pressure  made  upon  it.;  thus  acting  like 


THE    HUMAN    SKELETON, 


93 


an  Infinite  number  of  springs  of  the  most  delicate  structure. 
Besides  this,  the  foot  is  a  double  arch  ;  it  is  arched  from 
the  toes  to  the  heel,  and  from  side  to  side,  and  the  bones  are 
so  wedged  together,  and  bound  to  each  other  by  ligaments, 
that  solidity  is  combined  with  elasticity  and  lightness. 


55.  In  reviewing  the  human  skeleton,  we  cannot  but  re- 
mark the  nice  adaptation  of  all  the  parts  to  each  other,  and 
to  the  shares  which  they  have  respectively  to  bear  ;  how 
the  objects  of  strength  and  lightness  are  combined,  and  how 
the  nature  and  strength  of  material  in  different  parts  are  so 
admirably  adapted  to  the  purposes  which  the  parts  are 
designed  to  serve.  No  one  can  contemplate  the  marks  of 
wisdom  and  design  displayed  in  the  osseous  fabric,  without 
being  led  insensibly  to  acknowledge  the  hand  of  an  all-wise 
and  benevolent  Master  Builder. 


94  '  PHYSIOLOGY. 

Questions. — Of  how  many  bones  does  the  human  skeleton  consist  ? 
How  are  they  divided  ?     What  is  a  natural  skeleton  ?      What  an  arti- 
ficial ?     What  uses  does  the  skeleton  serve  ?     What  bones  are  said  to 
be  -symmetrical  ?     How  many  bones  are  there  in  the  head  ? — in  the 
trunk  ? — in  the  upper  extremities  ? — in  the   lower  ?     How  does  the 
skeleton  compare  with  works  of  human  art  ?     How  is  the  brain  pro- 
tected  from  injuries  ?     How  many  plates  do  the  bones  of  the  skull 
contain  ?     What    changes    does    age    produce   in   the   bones   of  the 
skull  ?     What  are  the  sutures  ? — what  their   use  ?      To  what   does 
Sir  Charles  Bell  compare  the  skull  ?     How  does  it  resemble  a  dome  ? 
What  are  the  principal  sutures  ?     Describe  the  frontal  bone.     What 
is   said   of   the   national    peculiarities    in    the    shape    of  the    head  ? 
What  shaped  heads  had  the  ancient  Egyptians  ?     Does  the   texture 
of  skulls  vary  ?     What  changes  occur  in   the  thickness  and  weight 
of   the   bones    of  the   skull  ?      What  is  said   of  the   cavity   of  ihe 
cranium?     What  is  formed  first,  the  brain  or  the  skull  ?     What  uses 
does  the  spine  serve  ?     Of  how  many  bones  does  it  consist  ?     What 
are  they  called  ?     How  divided  ?     Describe  a  vertebra.    What  sort  of 
substance  is  placed   between  the  vertebrae  ? — its  use  ?     Why  is  the 
spine  curved  like  an  /?     What  is  the  spine  disease? — its  causes? — 
its  cure  ?     What   effect  have  mechanical  remedies  ?     Do  boys  ever 
have  it  ?     Describe   the  thorax.     How  many  ribs  are  there  ?     What 
are  trite  ribs  ?     What  false  ?     Which  are  the  largest  ?     Where  is  the 
sternum  situated  ?     Describe  it.     What  is  the  use  of  the  cartilages 
between  the  sternum  and  ribs  ?     What  is  the  next  division  of  the 
trunk  ?     What  is  the  pelvis  ? — Of  how  many  bones  composed  ?    What 
its  use  ?     The  last  division  7     Where  is  the  clavicle  ? — its  use  ?     Des- 
cribe  the  scapula, — its  use  ?     Is  great  freedom  of  motion  compatible 
with  great  strength  in  a  joint?     Describe  the  os  humeri.     Of  how 
many  kinds  of  motion  susceptible  ?  Describe  the  fore  arm  ? — the  radius  ? 
— the  ulna.     What  is  the  contrivance  for  rotating  the  arm  ?     What  is 
the  olecranon  ? — its  use  ?     In  graminiverous   animals,  how  are  these 
bones   constructed  ?     How  can   the  anatomist  tell  to  what  kind  of 
animal  any  bone  belongs  ?     How  many  bones  are  there  in  the  hand  ? 
— how  many  in  the  wrist  ?     What  is  said  of  the  thumb  ? — Of  the 
fingers?     What  are  the  bones  of  the  lower  extremity?     Describe  the 
hip  joint? — the  knee.    Does  the  pressure  of  the  atmosphere  affect  the 
joints  ?     Describe  the  leg  below  the  knee?— the  ankle.     How  are  the 
bones  of  the  foot  divided  ?     How'  many  bones  in  the  tarsus  ? — the 
metatarsus  ? — the  phalanges  ? — the  foot  ?    What  is  the  use  of  so  many 
bones  ?     What  is  the  use  of  the  arched  form  of  the  foot  ? 


CHAPTER  VII. 

PROPERTIES    OF    ANIMAL    BODIES. 

1.  There  are  various  properties  which  distinguish  living 
from  dead  animal  matter.  Both,  in  common,  possess  certain 
•physical  properties,  such  as  weight,  extensibility,  flexibility^ 
6ic.  ;  but  living  matter  has  certain  physiological  or  vital 
properties  pecuUar  to  it.  It  is  these  which  bring  it  under 
the  influence  of  external  agents. 

2.  All  the  phenomena  of  life  are  the  effect  of  impressions 
made  upon  the  various  organs  of  the  body,  by  external  or 
internal  agents ;  and  each  organ  has  its  own  proper  sti- 
mulus. Thus  the  eye  is  stimulated  by  light ;  the  ear  by 
sound,  the  Jiose  by  odours,  the  organs  of  taste  by  condi- 
ments, &;c. 

3.  The  chick  in  its  shell  is  developed  by  the  influence  of 
heat ;  the  seed  germinates  under  the  combined  effect  of 
warmth  and  moisture  ;  and  so  the  growth  of  the  human 
body  requires  the  application  of  the  appropriate  stimulants, 
such  as  food,  drink,  air,  exercise,  &c. 

4.  Every  tissue  and  organ  has  its  own  mode  of  activity. 
For  example,  the  lungs  react  under  the  influence  of  the  air ; 
the  heart  under  that  of  the  blood  ;  the  muscles  under  that  of 
the  will ;  the  stomach  under  that  of  food,  <S£C.  Every  gland, 
though  supplied  by  the  same  blood,  is  excited  to  secrete  or 
form  that  particular  fluid  for  which  it  was  so  designed  ;  and 
why  the  liver  does  not  secrete  urine  and  the  kidneys  bile,  it 
were  useless  to  inquire. 

5.  This  property  of  living-  matter  has  three  principal 
modifications  in  the  solids  and  fluids,  which  have  been  called 
sensitive,  motive,  and  alterative.  By  the  sensitive  powers,  are 
meant  sensibility  and  its  modifications  ;  the  motive  are  con- 
tractility  and  expansibility ;  the  alterative  are   those  which 


96  PHYSIOLOGY. 

preside  over  the  formation   and   nutrition  of  the  different 
organs  and  tissues  of  the  body. 

6.  Sensibility  belongs  exclusively  to  animals  provided  with 
a  nervous  system.  It  enables  us  to  receive  impressions 
from  external  objects,  or  from  changes  going  on  in  our  own 
bodies  ;  and  to  the  accuracy  of  this  power,  we  owe  our 
ability  to  guard  ourselves  against  the  influence  of  noxious 
agents. 

7.  Sensibility  may  be  divided  into  two  kinds,  general  and 
special.  By  general  sensibility  is  meant,  that  uni ve  rsal  sense, 
of  which  we  are  conscious  over  the  whole  body,  in  the 
mouth,  &c.  The  same  also  exists  in  the  interior  of  the 
body,  and  conveys  to  the  mind  a  knowledge  of  the  wants  of 
the  system  ;  and  when  disease  attacks,  any  part,  it  immedi- 
ately apprizes  us  of  the  danger,  in  order  that  we  may  take 
early  measures  to  remove  it.  By  special  sensibility,  we 
mean  that  property  which  renders  the  eye  sensible  to  light, 
the  ear  to  sound,  &;c.  Every  organ  has  its  own  special 
sensibility. 

8.  The  brain  is  the  common  centre  of  sensibility,  both 
general  and  special.  No  impression  can  be  felt  on  any  part 
or  organ,  unless  it  has  a  connection  with  the  brain.  If  the 
nerves  going  from  that  organ  are  divided,  or  if  their  function 
is  lost  from  palsy  or  any  cause  whatever,  there  can  be  no 
sensation  perceived,  as  none  is  excited, 

9.  By  perception  is  meant,  the  faculty  which  the  brain 
has  of  perceiving  or  taking  notice  of  these  impressions. 
Perception  and  thought  then,  are  owing  to  the  property  of 
matter,  called  sensibility.  Without  it,  we  would  be  like 
stocks  or  stones,,  alike  unconscious  of  pleasure  or  of  pain. 

10.  According  to  some  physiologists,  there  is  another 
kind  of  sensibility,  which  is  termed  organic.  This  resides 
in  the  several  internal  organs,  where  it  i&  called  into  exer- 
cise, and  does  not  require  the  action  of  the  bi-ain.  It  de- 
pends for  nervous  influence  upon  the  great  sympathetic  nerve. 
That  such  a  kind  of  sensibility  exists  is  very  probable,  but 


PROPERTIES    OF    ANIMAL    BODIES.  97 

we  have  no  proof  of  its  existence  in  our  own  feelings  and 
consciousness,  as  we  have  of  the  other  kinds  of  sensibiUty. 

11.  By  organic  sensibiUty,  we  mean  that  the  stomach  is 
sensible  to  food,  the  heart  to  the  blood,  &c.  ;  and  that  this 
feeling  is  confined  to  the  organ  and  not  transmitted  to  the 
brain.  It  presides  over  the  process  of  digestion,  circulation, 
secretion,  absorption,  and  nutrition. 

12.  Although  the  internal  organs  of  the  body  are  not 
sensible  to  the  presence  of  the  fluids  or  solids  with  which 
they  are  usually  in  contact,  yet  if  foreign  bodies  are  brought 
in  contact  with  them,  or  substances  calculated  to  injure 
them,  we  are  immediately  made  sensible  of  it.  Thus  let  a 
person  drink  a  quantity  of  brandy,  or  spirits,  to  which  he 
is  not  accustomed,  and  he  will  at  once  feel  a  sensation  of 
heat  in  the  region  of  the  stomach,  altogether  unnatural  to 
that  organ.  This  proves  that  ardent  spirits  are  not  designed 
for  the  drink  of  man,  and  are  therefore  hurtful, 

13.  Certain  parts  of  the  body,  which,  in  a  healthy  state, 
are  nearly  insensible  ;  yet,  by  disease,  become  the  seats  of 
acute  pain.  This  is  particularly  the  case  with  the  bones, 
cartilages,  and  ligaments — parts  usually  wholly  destitute  of 
feeling. 

14.  Contractility,  or  the  propeHy  of  contracting,  is  the  chief 
motive  power  of  the  system.  It  exists  in  various  degrees,  in 
diflferent  kinds  of  animal  matter.  That  element  which  pos- 
sesses it  in  the  greatest  degree  is  Jihrin ;  and  those  tissues 
which  have  the  most  fibrin,  have  the  greatest  degree  of  con- 
tractility. The  same  is  true  of  muscles,  for  the  heart,  which 
is  in  constant  motion,  is  almost  pure  Jihrin. 

15.  It  is  supposed  that  the  coagulation  of  the  blood  is 
owing  to  this  contractile  power  of  fibrin.  In  the  living 
vessels,  the  blood  is  kept  fluid  by  the  vital  influence  of  the 
walls  of  the  vessels  themselves  ;  but  as  soon  as  it  is  with- 
drawn from  this  influence,  the  particles  of  fibrin  immediately 
rush  together  and  form  a  solid  mass. 

16.  Those  tissues  which  contain  but  little  fibrin  and  are 

9 


98  PHYSIOLOGY. 

made  up  mostly  of  gelatine,  as  the  membranes,  cartilages, 
skin,  vessels,  &;c.,  have  but  a  slight  degree  of  contractility  ; 
that  they  possess  it,  in  some  measure,  is  evident  from  the 
contraction  of  blood-vessels  by  the  application  of  stimulants. 

17.  There  are  two  modifications  of  contractility  ;  one  of 
which  depends  for  its  exercise  on  the  brain,  and  the  other 
does  not.  For  example,  if  we  wish  to  bend  the  arm,  we  have 
but  to  transmit  to  the  muscles  of  the  arm,  throuo-h  the  nerves 
with  which  it  is  supplied  from  the  brain,  a  volition,  or  act 
of  the  will,  to  that  effect,  and  the  arm  bends.  Here  we  per- 
ceive that  the  influence  of  the  brain  is  necessary  to  contrac- 
tility  or  motion. 

18.  When  certain  muscles  are  deprived  of  this  power  of 
contracting,  they  are  said  to  be  paralyzed,  or  the  limb  is 
called  paralytic.  When  they  have  it  in  excess,  they  are  in 
a  state  of  spasm,  or  convulsion.  We  see  such  a  state  often 
brought  on  by  excessive  drinking.  There  is  no  cure  for  this 
but  by  entirely  breaking  off  the  habit. 

19.  The  other  kind  of  contractility  belongs  to  every  part 
of  the  body.  It  does  not  depend  for  its  existence  on  the 
brain,  nor  is  it  at  all  under  the  influence  of  the  will,  or 
accompanied  with  consciousness.  Thus  the  heart  and  the 
stomach  contract  constantly  under  the  application  of  their 
proper  stimuli,  but  the  brain  is  not  conscious  of  it ;  their 
action  is  entirely  beyond  its  jurisdiction.  This  form  of  con- 
tractility has  been  called  insensible. 

20.  It  is  owing  to  the  insensible,  organic  contractility, 
that  the  blood  circulates  in  the  capillary  vessels  ;  the  lymph 
and  the  chyle  in  the  absorbents  and  lacteals,  and  all  the 
secreted  fluids  through  the  vessels  that  prepare  them.  In 
all  animals  destitute  of  a  heart,  the  fluids  can  only  be  moved 
by  this  insensible  contractile  power.  A  similar  force  is 
supposed  to  exist  in  the  vessels  of  plants, 

21.  These  two  kinds  of  contractility,  viz.,  the  sensible 
and  insensible,  have  been  compared  to  the  hour  and  minute 
hands  on  the  dial  of  a  clock,  which  are  both  moved  by  the 


PROrERTIES    OF    ANIMAL    BODIES.  99 

same  power  ;  yet  the  motion  of  one  is  insensible  to  the  eye, 
while  that  of  the  other  is  distinctly  visible. 

22.  By  means  of  the  alterative  powers,  all  the  changes 
which  take  place  in  the  composition  of  the  solids  and  fluids 
of  the  body  are  effected.  By  these,  the  food  is  changed  into 
chyme,  and  then  into  chyle  ;  chyle  into  blood,  and  blood  into 
bone,  muscle,  cartilage,  &c.  By  these,  animal  heat  is  pre- 
served uniform  ;  and  the  solids  preserve  their  cohesion,  and 
the  fluids  their  fluidity.  In  short,  it  is  these  powers  that 
for  a  time  successfully  resist  the  agency  of  chemical  laws. 

23.  Some  physiologists  attempt  to  account  for  every  thing 
that  takes  place  in  the  body,  on  chemical  or  mechanical 
principles.  But  the  vital  laws,  or  organic  forces,  form  corn- 
pounds  which  could  never  be  produced  by  chemical  affinity. 
In  fact,  they  are  antagonistic  forces,  fighting  against  each 
other.  The  chemist  can  decompose  blood,  bile,  saliva,  al- 
bumen, gelatine,  and  fibrin,  but  he  can  not  re-form  one  of 
them.  He  can  no  more  make  a  piece  of  bone,  than  he  can 
make  a  diamond. 

24.  The  physical  properties  of  the  animal  tissues  are 
usually  reckoned  as  five  in  number,  viz.  elasticity,  extensibiU 
ity,  Jlexihility,  imbibition,  and  evaporation, 

25.  Elasticity  is  one  of  the  physical  properties  of  animal 
matter.  It  is  that  power  which  tends  to  restore  parts  that 
have  been  stretched  or  extended  to  their  former  state.  It  is 
possessed  in  the  greatest  degree  by  the  cellular  tissue,  which 
enters  largely  into  the  composition  of  all  the  structures  in 
the  body.  All  the  organs  and  membranes  of  the  body  are 
in  a  constant  state  of  extension.  All  the  hollow  organs,  as 
the  stomach,  gall-bladder,  and  blood-vessels  are  kept  distend- 
ed by  the  volume  of  their  contents.  The  extensor  and 
flexor  muscles,  when  in  a  state  of  inaction,  are  in  a  state  of 
extension.  If  such  were  not  the  case,  all  the  organs  would 
contract  and  shrink  to  a  comparatively  small  size. 

26.  When  the  stomach  is  empty,  its  sides  contract  till 
they  almost  touch  each  other.     When  a  muscle  is  cut,  the 


100  PHYSIOLOGY. 

wound  gapes  open,  owing  to  the  two  parts  receding.  The 
cartilages  of  the  ribs  are  highly  elastic,  and  this  facilitates 
much  the  function  of  respiration.  The  same  is  true  of  the 
substance  of  the  lungs  themselves.  The  cartilages  between 
the  bones  and  the  spine  are  highly  elastic.  The  loss  of  this 
elasticity  makes  a  difference  of  an  inch  or  more  between  the 
height  of  a  man  in  the  morning  and  at  evening.  It  is 
not  unusual  for  a  very  tall  person  to  lose  an  inch  in  height 
by  dancing  all  the  evening.  During  sleep,  the  force  of 
elasticity  restores  these  cartilages  to  their  usual  dimen- 
sions. 

27.  The  elasticity  of  the  arteries  contributes  much  to  the 
circulation  of  the  blood.  The  blood  as  it  is  forced  into  these 
vessels,  is  constantly  reacted  upon,  by  their  elastic  coats, 
and  in  this  way  driven  along  towards  their  termination  in 
the  capillary  vessels.  The  same  power  assists  in  circulating 
the  lymph  and  chyle  in  the  vessels  which  contain  them.  It 
is  the  last  function  that  ceases  to  act,  and  it  is  not  wholly 
destroyed  even  at  death. 

28.  Flexibility  and  extensihility  are  properties  existing  in 
various  degrees  in  different  parts  of  the  body.  The  liga- 
ments, or  little  bands,  which  tie  together  the  bones,  are  more 
flexible  than  any  other  part.  By  observing  the  astonishing 
feats  of  the  rope-dancer,  we  see  how  flexible  these  parts  are* 
The  tendons  which  connect  muscles  with  the  bones  they 
move,  are  capable  of  little,  if  any  extension.  If  they  stretch- 
ed, when  the  muscles  to  which  they  belong  contract,  the 
limbs  would  not  move,  and  the  moving  force  would  thus  be 
lost. 

29.  Imbibition,  is  another  power  possessed  by  living  animal 
bodies.  It  means  the  act  of  drinking  in,  or  taking  up  fluids, 
which  may  be  in  contact  with  any  part.  For  example,  if  a 
certain  fluid  be  placed  in  contact  with  an  animal  tissue,  it 
will  penetrate  into  the  latter,  as  water  would  into  a  sponge, 
and  this  property  is  possessed  by  all  the  soft  tissues  to  a 
greater  or  less  extent.     All  the  serous  membranes  absorb 


PROPERTIES  OF  ANIMAL  BODIES.        101 

with  great  facility.  The  epidermis  or  cuticle  of  the  skin 
permits  fluids  to  pass  with  difficulty.  That  water  is  taken 
up  in  considerable  quantity,  however,  is  proved  by  the  fact, 
which  has  often  been  proved  by  experiment,  that  a  man  in- 
creases in  weight  by  remaining  for  a  considerable  time  in  a 
warm  bath. 

30.  The  following  experiments  prove  the  nature  of  this 
process.  If  we  fill  the  intestine  of  a  chicken  with  milk,  and 
place  it  in  water,  we  shall  see  the  milk  pass  through  its 
coats  into  the  water,  and  the  water  will  pass  through  in  an 
opposite  direction  to  supply  its  place.  In  the  same  manner, 
if  a  bladder  be  filled  with  hydrogen  gas,  and  suspended  in 
the  air,  in  a  short  time  it  will  be  found  to  be  mixed  with 
atmospheric  air,  which  has  passed  through  its  coats.  The 
result  of  all  the  experiments  on  this  subject  seems  to  show, 
that  when  any  cavity  containing  a  fluid  is  immersed  in 
another  fluid  less  dense  than  the  former,  there  is  a  tendency 
in  the  membrane  to  expel  the  denser,  and  absorb  the  thinner 
fluid. 

31.  Many  of  the  animal  tissues  are  indebted  for  their 
physical  properties  to  the  water  they  imbibe.  If  they  are 
deprived  of  this  water,  they  are  unable  to  perform  their 
proper  office  and  function,  until  they  are  again  supplied  with 
it.  Hence  one  important  reason  why  the  system  craves 
water,  and  why  the  want  of  it  produces  such  distressing 
effects. 

32.  By  the  functions  of  man,  we  understand  the  opera- 
tion of  the  various  organs  ;  in  other  words,  his  vital  actions » 
Life  is  made  up  of  a  constant  series  of  these  actions,  from 
the  period  of  birth  to  the  moment  of  dissolution.  Physiol- 
ogists have  attempted  to  define  life  ;  but  the  best  definition  we 
can  give  is,  that  it  is  an  assemblage  of  actions.  Indeed,  the 
essential  nature  of  life  is  an  impenetrable  mystery,  and  not 
a  proper  subject  for  philosophical  inquiry.  As  the  fluids 
are  as  much  endowed  with  life  as  the  solids,  it  cannot  be 
:said  that  life   is  the  "  eflfect  of  organization  ;"  besides,  ^ 

9* 


102  PHYSIOLOGY. 

dead  man  has  the  same  organization  as  when  alive.  It 
is,  therefore,  far  better  to  confess  our  ignorance,  and  say 
with  John  Hunter, — "  Ufe  is  a  property  we  do  not  under- 
stand." 

33.  All  the  actions  or  functions  of  the  body  are  mutually 
dependent  on  each  other.  They  constitute  a  circle,  with- 
out beginning  or  end.  The  motion  of  the  blood  depends  on 
the  action  of  the  heart  and  arteries  ;  the  action  of  the  heart 
and  arteries  depends  on  the  presence  of  blood.  The  heart 
cannot  act  without  the  action  of  the  lungs  ;  the  lungs  can- 
not act  without  the  action  of  the  heart.  Neither  lungs  nor 
heart  can  act  without  the  influence  of  the  brain  ;  the  brain 
would  have  no  influence,  v/ere  it  not  for  the  action  of  the 
iungs  and  heart.. 

34.  Thus  the  steam  of  a  steam-engine  works  a  bellows 
which  blows  a  fire  that  produces  the  steam.  It  would  be  as 
difl[icult  in  this  case,  as  in  that  of  the  animal  functions  to 
say,  which  of  these  might  be  easiest  dispensed  with.  If  we 
spare  the  bellows,  the  fire  will  not  burn  ;  if  we  spare  the  fire, 
the  steam  will  not  be  raised  ;  if  we  spare  the  steam,  the  bel- 
lows will  not  be  worked  ;  so  that  if  we  spare  either  fire,  bel- 
lows, or  steam,  the  machinery  must  stop.  So  it  is  in  the 
human  body. 

35.  The  functions  which  fall  within  the  scope  of  this 
work  to  notice,  may  be  divided  into  three  classes  ;  1,  vital ; 
2,  nutritive  ;  and  3,  sensorial.  The  vital  functions  are  those 
which  are  every  moment  essential  to  preserve  life.  They 
also  may  be  considered  as  three  in  number,  viz  :  innerva- 
tioUf  circulation,  and  respiration ;  or  the  functions  of  the 
nervous  system,  those  of  the  heart,  and  those  of  the  lungs. 

36.  The  nutritive  functions  preside  over  the  growth  and 
nutrition  of  the  body.  By  their  influence,  the  food  is  as- 
similated, and  becomes  a  part  of  our  structures  ;  while  all 
the  waste  materials  and  worn-out  elements  are  expelled  from 
the  system.  It  thus  embraces  four  functions ;  digestion^ 
•absorption,  nutrition,  and  secretion. 


-   PROPERTIES    OF    ANIMAL    BODIES.  103 

37.  The  sensorial  functions  are  sometimes  called  the 
functions  of  relation,  because  it  is  through  them  that  we 
hold  communication  with  the  external  world.  They  com- 
prise the  sensations,  intellectual  operations,  and  voluntary 
Qnotion^,  It  is  the  sensorial  functions  that  raise  man  above 
all  other  animals.  In  proportion  as  they  are  more  or 
less  perfect^  organized  beings  ascend  or  descend  in  the 
scale  of  existence.  In  the  lower  animals,  they  are  limit- 
ed to  the  circle  of  physical  wants  ;  but  in  man,  they  con- 
fer moral  and  intellectual  faculties,  which  are  his  noblest 
attributes. 

38.  These  functions  have  the  brain  as  their  common 
•centre.  They  can  be  improved  to  an  almost  indefinite 
degree  by  education  and  habit.  We  see  this  in  the  perfec- 
tion wMch  some  of  the  senses  acquire  when  others  are  lost ; 
in  the  gigantic  intellect  of  a  Newton  or  a  Locke,  whose 
mental  efforts  at  first  were  probably  as  weak  as  those  of 
other  men.  In  all  such  cases,  individuals  acquire  superi- 
ority chiefly  by  education  and  constant  practice. 


Questions. — How  is  living  animal  matter  distinguished  from  dead  ? 
What  properties  are  possessed  in  common  ?  What  are  the  phenomena 
of  hfe  owing  to  ?  What  developes  the  chick  ?  What  properties  does 
living  matter  possess  ?  What  is  understood  by  the  sensitive  powers  ? 
— the  motive  ? — the  alterative  ?  What  characterizes  animals  provided 
with  a  nervous  system  ?  How  many  kinds  of  sensibility  are  there  ? 
What  is  meant  by  general  sensibility  ? — by  special  ?  What  is  the 
common  centre  of  sensibility  ?  What  is  perception  1  What  is  organic 
sensibility  ?  Are  the  internal  organs  sensible  to  the  presence  of  their 
^jontents  ?  How  are  such  parts  affected  by  disease  ?  What  is  con. 
tractility  ?  What  element  possesses  it  in  a  great  degree  ?  How  many 
kinds  of  contractility  are  there  ?  When  is  a  limb  said  to  be  paralytic  ? 
When  in  spasm  ?  What  are  the  alterative  powers  ?  What  their  use  ? 
Is  the  body  under  the  influence  of  chemical  laws  ?  What  are  the 
physical  properties  of  the  animal  tissues  ?  What  office  does  elasticity 
perform  ?  Describe  its  operation  in  cartilages,  arteries,  &,c.  What 
are  the  uses  of  flexibility  and  extensibility  in  the  animal  body  ?  What 
is  imbibition  ?     Do  the  serous  membranes  absorb  ?    What  experiments 


104  PHYSIOLOGY-. 

prove  im"bibition  ?  What  are  understood  by  the  functions  of  raan  ? 
What  is  life  '?  Are  the  fluids  alive  as  well  as  the  solids  ?  Are  the 
functions  of  the  body  dependent  on  each  other  ?  Illusti-ate  this  de- 
pendence ?  How  are  the  functions  divided  ?  What  are  vital  func- 
tions ? — nutritive  ? — sensorial  ?  What  raises  man  above  all  other  ani- 
mals  ? 


CHAPTER  VIII. 

RELATION  OF  ANIMAL  BODIES  TO  HEAT,  LIGHT,  AND 
ELECTRICITY. 

1.  The  relations  which  animal  bodies  have  to  heat,  light, 
and  electricity,  are  highly  interesting,  and  worthy  of  particu- 
lar notice.  To  a  certain  extent,  all  animal  bodies  have  the 
power  of  regulating  their  own  temperature.  Many  of  them 
develope  electricity  ;  and  some  of  them,  like  the  lighlning-. 
hug,  and  other  insects,  can  produce  light.  These  are  singu- 
lar properties  of  living  animal  matter. 

2.  The  heat  of  animal  bodies  is  produced  within  them- 
selves. It  is  not  received  from  without,  nor  can  it  be  ;  as 
the  natural  temperature  of  the  body  is  near  100  degrees  ; 
even  when  the  temperature  of  the  surrounding  air  is  below 
zero.  How  this  is  produced  we  shall  inquire  when  we  come 
to  treat  especially  of  animal  heat. 

3.  Plants  have  a  lower  temperature  than  animals,  and  the 
higher  animals  are  in  the  scale  of  organized  beings,  so  much 
the  more  animal  heat  do  they  produce.  Thus  the  tempera- 
ture of  what  are  called  the  cold-blooded  animals,  such  as 
fishes,  is  not  much  above  that  of  the  water  in  which  they 
live ;  and  although  they  do  not  often  freeze  to  death  in  the 
winter,  yet  they  become  so  torpid  as  to  be  incapable  of  mo- 
tion. 

4.  It  is  a  favourite  sport  in  New  England  in  the  winter 
season,  to  hunt,  on  skates,  for  the  pickerel,  and  other  fish, 
which  abound  in  the  lakes  and  ponds  ;  and  when  found  to 
take  them,  by  cutting  through  the  ice  with  a  hatchet ;  and 
to  spear  them  by  torchlight  at  night.  Now  had  they  the 
faculty  of  producing  animal  heat,  like  quadrupeds,  or  birds, 
or  man,  they  would  not  be  rendered  torpid  and  incapable  of 
motion  by  cold. 


106  PHYSIOLOGY. 

5.  Living  animal  bodies  have  not  only  the  faculty  of  pro- 
ducing heat,  but  they  can  also  resist  heat  of  a  much  higher 
temperature  than  their  own  bodies.  The  heat  of  the  body 
is  kept  at  its  usual  standard  of  98  degrees,  by  the  exhalent 
vessels  of  the  skin,  which  absorb  by  means  of  the  perspira- 
tion the  excess  of  caloric,  and  fly  off  with  it  in  a  state  of 
vapour. 

6.  In  very  hot  weather,  those  functions  of  the  body,  such 
as  digestion,  nutrition,  and  secretion,  on  which  the  produc- 
tion of  animal  heat  depends,  are  weakened  by  the  excessive 
heat,  so  that  in  fact  less  caloric  is  produced  in  the  system 
than  in  cold  weather.  This  is  a  wise  provision  of  Providence, 
that  when  much  internal  heat  is  wanted  to  guard  against  the 
cold,  it  is  produced  ;  when  less  is  needed,  on  account  of  the 
warmth,  the  system  generates  less. 

7.  Animal  bodies  are  also  capable  of  developing  electrieity  •, 
as  most  of  the  bodies  which  surround  us  are  conductors  of 
the  electric  fluid,  it  generally  passes  off*  as  fast  as  it  is 
formed.  Sparks  of  fire,  however,  are  often  seen  in  winter, 
on  taking  off"  in  the  dark,  silk  dresses  or  stockings,  or  flannel 
drawers.  Some  physiologists  maintain  that  the  nervous 
power  is  nothing  but  the  electric  fluid  ;  but  though  this  may 
not  be  admitted,  there  is  a  very  close  analogy  between  them. 

8.  It  has  also  been  found  that  needles  plunged  into  the  mid- 
dle of  a  nerve,  become  magnetic,  and  are  capable  of  attracting 
light  substances,  such  as  pieces  of  paper  ;  and  a  physiologist 
by  the  name  of  Weinhold  says,  that  he  has  seen  sparks 
obtained  by  bringing  the  divided  ends  of  a  nerve  together. 
Muller  mentions  in  his  late  work  on  Physiology,  that  effi- 
cient galvanic  piles  can  be  constructed  from  organic  sub- 
stances, without  any  concurrence  of  metals.  Concentrated 
solutions  of  organic  substances  were  spread  upon  thin  paper, 
and  with  disks  of  this,  paper  piles  constructed,  the  two  layers 
of  different  substances  being  separated  by  two  thicknesses  of 
paper  ;  electricity  was  developed  by  these  piles,  and  tested 
by  an  electrometer.     It  would  seem  from  these  experiments, 


RELATION  OF  ANIMAL  BODIES  TO  HEAT,  6CC.         107 

that  the  nervous  system  is  capable  of  developing  electricity, 
under  the  influence  of  vitality. 

9.  Certain  fishes,  such  as  the  torpedo,  the  electrical  eel, 
and  five  or  six  other  species,  are  provided  with  special  organs 
for  the  production  of  electricity.  In  the  torpedo  they  consist 
of  a  largo  number  oi^ prisms,  of  from  three  to  six  sides,  stand- 
ing close  together,  near  the  gills  of  the  fish,  and  perpendicu- 
lar to  the  surface.  They  are  composed  of  membranous 
tubes,  divided  into  numerous  transverse  cells,  abu-ndantly 
supplied  with  blood  vessels  and  nerves.  These  vessels  are 
filled  with  a  fluid  of  an  albuminous  nature.  These  organs 
are  connected  with  the  brain  by  three  large  nerves  on  each 
side. 

10.  In  the  gymnotus  the  electrical  apparatus  may  be  com- 
pared to  a  battery  of  galvanic  troughs.  Two  of  these  are 
found  on  each  side  of  the  spine,  separated  from  each  other  by 
a  long  ligament,  and  extending  the  whole  length  of  the  fish. 
They  are  composed  of  horizontal  membranous  plates,  sepa- 
rated from  one  another  by  a  small  interval,  and  crossed  in  a 
perpendicular  direction  by  membranous  partitions,  so  as  to 
form  a  great  number  of  cells,  which  are  filled  with  a  gelati- 
nous fluid.  These  organs  receive  numerous  branches  and 
nerves  from  the  spinal  marrow. 

11.  The  resemblance  of  these  organs  to  the  galvanic  pile 
is  very  striking.  The  latter  consists  of  alternate  plates  of 
copper  and  zinc  with  a  fluid  between  them.  Thus  we  have 
in  these  fishes  alternate  layers  of  membranous  partitions  and 
albuminous  fluid.  But  is  is  worthy  of  particular  notice  that 
these  organs  lose  their  electric  powers  if  the  nerves  which 
supply  them  are  divided.  There  can  be  no  doubt  then,  that 
the  electric  shock  which  they  give  is  a  vital  act,  depending 
on  a  nervous  influence,  and  under  the  control  of  the  animal's 
will. 

12.  The  sensation  produced  by  the  shock  of  an  electrical 
fish,  is  also  similar  to  that  of  common  electricity.  It  is  pow- 
erful enough  to  kill  small  fishes,  and  is  the  animal's  weapon 


108  PHYSIOLOGY. 

of  defence.  Sparks  also  have  been  seen  to  attend  the  dis- 
charges ;  and  the  shock  has  been  communicated  through  a 
chain  consisting  of  several  persons  with  their  hands  joined. 

13.  Common  electricity,  and  that  produced  by  the  organs 
of  electric  animals,  are  generally  believed  to  be  different,  but 
it  has  lately  been  discovered  by  Dr.  Davy,  that  the  electric 
organs  of  the  torpedo  affect  the  galvanometer,  render  needles 
magnetic,  and  decompose  v^^ater. 

14.  Many  animals  as  well  as  plants  are  endowed  with 
phosphorescent  properties.  Every  person  almost,  has  seen 
rotten  wood,  or  dead  fish,  shine  in  the  dark ;  such  are  phos- 
phorescent. This  phenomenon  is  probably  owing  to  the 
fact,  that  during  the  decomposition  of  animal  or  vegetable 
matter  there  is  formed  a  highly  inflammable  compound  of 
carbon,  hydrogen,  and  oxygen,  which  like  phosphorous,  burns 
at  the  ordinary  temperature  of  the  air,  with  an  evolution  of 
light. 

15.  But  several  living  animals  exhibit  luminous  appear- 
ances. Many  of  the  lower  order  of  animals  that  inhabit  the 
sea,  and  some  fishes,  are  phosphorescent.  It  is  this  that 
causes  the  luminous  appearance  of  the  ocean  in  warm  cli- 
mates. If  a  vessel  be  filled  with  sea- water  containing  these 
animalcula  they  immediately  become  phosphorescent,  on 
shaking  the  vessel. 

16.  It  is  not  uncommon  to  find  insects  which  have  the 
faculty  of  phosphorescence  in  a  high  degree.  It  is  supposed 
to  reside  in  a  peculiar  albuminous  principle,  secreted  by  the 
animal,  and  that  it  requires  for  its  manifestation  atmospheric 
air  and  a  certain  degree  of  heat.  It  is  evidently  under  the 
control  of  the  animal's  will,  and  probably  depends  on  the 
nervous  action.  Some  say,  however,  that  it  is  a  peculiar 
animal  matter  secreted  at  will,  which,  combining  with  the 
oxygen  of  the  air  gives  rise  to  the  disengagement  of  light. 


Questions. — Have  bodies  the  faculty  of  regulating  their  own  temper- 


RELATION  OF  ANIMAL  BODIES  TO  HEAT,  &C.  109 

ature  ?  What  is  said  of  animal  heat  ?  What  is  the  temperature  of 
cold  blooded  animals  ?  What  preserves  the  heat  of  the  body  uniform  ? 
Is  as  much  heat  produced  in  the  body  in  hot  as  in  cold  weather?  Do 
animal  bodies  develope  electricity.  Can  galvanic  piles  be  made  of  ani- 
mal  substances  alone  ?  What  kind  of  fish  are  electrical  ?  Describe  the 
electrical  apparatus  of  the  torpedo.  What  is  a  galvanic  pile  ?  What 
effects  have  the  electrical  discharges  of  the  torpedo,  &-c.  ?  In  what 
respects  like  common  electricity  ?  What  is  said  of  the  phosphorescent 
properties  of  animals?  What  animals  have  this  property?  What 
does  it  depend  on  ? 

10 


CHAPTER  IX. 

THE    NERVOUS    SYSTEM. 

The  Brain,  Spinal  Marrow,  and  Nerves. 

1.  There  is  no  subject,  which  falls  within  the  range  of 
physiological  enquiry,  more  interesting  or  more  important, 
than  that  of  the  nervous  system.  It  is  this  which  furnishes 
the  material  instrument  of  thought,  the  means  by  which  we 
become  acquainted  with  the  external  world  around  us,  and 
also  the  channels  by  which  the  will  sends  forth  its  commands 
to  the  instruments  it  employs  in  their  execution.  Besides 
this,  it  presides  over  and  regulates  the  functions  of  the  ani- 
mal economy,  and  binds  the  various  organs  into  one  sympa- 
thizing, harmonious  whole. 

2.  The  nervous  system  may  be  considered  as  embracing, 
1st.  the  brain  ;  2d.  the  medulla  oblongata  ;  3d.  the  spinal 
marrow  ;  4th.  the  nerves ;  5th.  the  ganglia.  These  are  all 
embraced  under  two  general  departments,  the  first  consisting 
of  the  brain  and  its  dependencies  ;  and  the  second,  of  the 
ganglia  and  their  nervous  connections  ;  the  first  appertain- 
ing particularly  to  animal  life,  conveying  impressions  calcu- 
lated to  produce  sensations,  and  sending  out  volitions  to  its 
servants,  the  organs  destined  to  receive  them  ;  while  the 
second  supply  those  organs  not  under  the  influence  of  the 
will,  viz.  of  digestion,  circulation,  respiration,  and  the  secre- 
tions. 

3.  These  two  grand  divisions  of  the  nervous  system, 
may  be  still  further  distinguished  by  the  circumstance,  that 
the  first,  or  cerebral  department,  is  exactly  symmetrical. 
The  nerves  all  go  out  in  pairs  from  each  side  of  the  brain 
and  spinal  cord,  while  the  ganglionic  system  of  nerves  is  dis- 
tributed irregularly  to  all  the  internal  organs.     The  nerves 


THE    NERVOUS    SYSTEM.  Ill 

of  the  first  kind,  are  either  nerves  of  sensation  or  of  motion. 
These  nerves,  as  discovered  by  Sir  Charles  Bell,  are  entirely 
distinct,  the  one  rarely,  if  ever,  performing  the  function  of 
the  other.  Although  these  nerves  are  endowed  with  different 
properties,  the  common  function  of  both  is,  to  give  us  correct 
intelligence  of  the  relative  condition  of  our  existence. 
When  these  functions  are  interrupted,  as  in  apoplexy,  or 
concussion  of  the  brain,  the  individual  is  deprived  of  all  feel- 
ing and  sensibility,  hence  they  are  called  the  nervous  depart- 
ment of  external  or  animal  life.  The  nervous  filaments 
which  furnish  the  power  of  motion,  arise  from  the  anterior 
column  of  the  spinal  marrow,  while  those  in  which  sensation 
resides,  are  connected  with  the  posterior  column. 

4.  The  brain  fills  the  cavity  of  the  cranium  or  skull,  and 
in  an  adult  weighs  between  three  and  four  pounds.  Its 
greatest  length  is  about  six  inches,  and  its  breadth  five 
inches,  though  its  dimensions  vary  greatly  in  different  per- 
sons. In  infancy  its  texture  is  soft,  but  it  grows  harder  in 
proportion  to  the  age.  The  brain  is  chiefly  composed  of 
two  distinct  parts,  the  cerebrum,  or  brain  proper ;  and  the 
cerebellum,  or  the  little  brain.  These  again  are  divided, 
each  into  two  distinct  lobes.  The  medulla  oblongata  is  the 
commencement  of  the  spinal  marrow. 

5.  The  brain  is  surrounded  by  three  membranes  ;  the  two 
inner  ones  thin  and  delicate  ;  the  outer  one  thick  and  firm, 
and  called  duj'a  mater.  It  is  a  perpendicular  fold  of  the  dura 
mater,  and  divides  the  brain  into  two  hemispheres.  It  ad- 
heres loosely  to  the  bones  of  the  skull ;  the  internal  perios- 
teum of  v.'hich  it  forms. 

6.  The  other  two  thin  membranes  are  called  arachnoid  and 
pia  mater.  The  first  is  a  serous  membrane,  as  the  dura  mater 
is  n  fibrous  membrane  ;  and  forms  a  completely  closed  sac  or 
bag.  This  membrane,  which  derives  its  name  from  its 
resemblance  j:o  a  spider's  web,  spreads  over  the  whole  surface 
of  the  brain,  without  dipping  into  any  of  its  furrows  or  con- 


112 


PHYSIOLOGY. 


volutions,  and  also  forms  a  sheath  for  all  nerves  or  blood, 
vessels  that  pass  out  of,  or  into  the  brain. 


a.  The  scalp,  turned  down. 

b.  The  cut  edge  of  the  bones  of  the  skull. 

e.  The  external  strong  membrane  of  the  brain,  (dura  mater)  sub 
pended  by  a  hook, 

d.  The  left  hemisphere  of  the  brain,  showing  its  convolutions. 

e.  The  superior  edge  of  the  right  hemisphere. 
/.  The  fissure  between  the  two  hen>ispheres. 


7.  The  pia  mater  is  a  loose  cellular  membrane,  composed 
chiefly  of  blood  vessels,  which  dips  into  all  the  fissures,  and 
wraps  round  all  the  convolutions  of  the  brain.  The  chief 
use  of  these  membranes  seems  to  be  to  support  the  different 
parts  of  the  brain  in  their  respective  places,  so  that  they  may 
not  be  injured  by  sudden  shocks  and  jars,  or  by  compression  ; 


THE    NERVOUS    SYSTEM.  113 

to  moisten  the  brain  ;  and  furnish  a  medium  of  transmitting 

blood  vessels  and  absorbents. 

8.  The  outside  surface  of  the  brain  is  cut  up,  or  inter- 
sected by  deep  winding  fissures,  forming  numerous  irregular 
eminences  called  convolutions.  These  fissures  are  generally 
about  an  inch  deep.  The  brain  on  the  outer  surface,  is  to  a 
considerable  depth  of  a  grey  or  ash  colour  ;  hence  it  is  called 
the  cineritious  or  ashy  portion,  and  sometimes  cortical,  from 
its  position,  like  the  bark  surrounding  a  tree.  The  internal 
portion  is  white,  and  is  therefore  called  the  medullary  part  of 
the  brain. 

9.  The  cortical  part  of  the  brain  which  is  found  on  the 
exterior  surface,  is  on  an  average  about  one-sixth  of  an  inch 
in  depth,  and  dips  down  every  where  between  the  convolu- 
tions. Besides  its  being  of  a  greyish  colour,  it  is  of  a  firmer 
consistence  than  the  medullary  matter.  It  is  full  of  vessels, 
and  from  this  circumstance  has  been  supposed  to  nourish  the 
medullary  part. 

10.  There  are  four  cavities  in  the  substance  of  the  brain, 
termed  ventricles.  Of  these  the  two  laieral  ventricles  are  the 
largest.  Daring  life  a  serous  exhalation  is  constantly  going 
on  into  their  interior,  and  in  health  this  fluid  is  absorbed  or 
taken  up,  as  fast  as  it  is  secreted.  In  dropsy  of  the  brain, 
the  water  sometimes  accumulates  in  these  cavities  in  im- 
mense quantities.  Not  long  since,  a  child,  about  ten  years 
of  age,  was  -exhibited  in  this  city,  whose  head  measured  two 
feet  and  seven  inches  in  circumference,  just  above  the  ears. 
The  head  was  so  heavy  he  could  not  raise  it  from  the  pil- 
low.  This  was  owing  to  water  in  the  ventricles.  The  med- 
ullary or  white  matter  of  the  brain  occupies  the  interior  part 
of  that  organ.  It  makes  up  by  far  the  largest  portion,  and 
is  fibrous  in  its  structure. 

11.  The  cerebellum  or  little  brain,  is  situated  at  the  base 
and  back  part  of  the  skull,  and  in  weight  it  is  only  about  one- 
eighth  or  ninth  part  of  that  of  the  cerebrum.  Like  the  large 
brain,  it  is  divided  into  two  lateral  halves.     It  is  made  up  of 

10* 


114  PHYSIOLOGY. 

several  little  lobes,  and  if  the  two  hemispheres  be  divided  l]y 
a  knife,  a  beautiful  appearance  is  presented,  resembling  the 
trunk  and  branches  of  a  tree  ;  composed  of  the  white  and 
grey  matter  of  the  brain.  From  its  shape  it  has  been  called 
arhor  vitcB,  or  tree  of  life, 

12.  The  Spinal  marrow  is  a  round  cord  of  nervous  matter 
which  passes  down  through  the  spine  to  the  loins.  It  is  di- 
vided into  two  equal  lateral  parts,  by  a  deep  fissure  or  groove, 
which  runs  through  its  whole  length  both  on  its  front  and 
back  surface.  Some  say  that  it  consists  of  four  distinct 
<:olumns  ;  others  that  it  is  made  up  of  six  white  strands,  two 
before,  two  behind,  and  two  on  the  sides  ;  proceeding  from 
the  cerehrum,  the  restiform  bodies,  and  the  cerebellum. 

13r.  There  are  forty-three  pair  of  nerves,  making  86  in  all, 
proceeding  from  the  brain  and  spinal  marrow.  These 
nerves  run  to  every  part  of  the  system,  conveying,  as  already 
stated,  all  sensations  and  impressions  to  the  brain,  and  also 
volition  from  the  brain,  to  all  the  voluntary  muscles  of  the 
body.  Of  these,  two  pair  go  from  the  cerebrum,  viz.,  those 
for  smell  and  sight,  or  the  olfactory  and  optic  ;  five  pair  go 
from  the  pons  varolii,  which  is  that  round  mass  of  nerve, 
which  lies  between,  and  seems  to  connect  the  cerebrum  and 
cerebellum.  Of  these,  the  third,  fourth,  and  sixth  pair  go  to 
the  muscles  of  the  eye  ;  while  the  ffth  and  seventh  are  dis. 
tributed  over  the  face. 

14.  The  remaining  thirty-six  pairs  go  out  from  the  spinal 
marrow,  \\z.,five  from  the  medulla  oblongata  ;  eight  from  the 
cervical ;  twelve  from  the  dorsal ;  five  from  the  lumbar  ;  and 
six  from  the  sacral  portion  of  the  spinal  cord.  These  nerves 
supply  filaments  to  every  muscular  fibre  in  the  system  ;  or 
pass  directly  to  the  organs  of  sense  without  sending  ofi"  twigs; 
some  of  them  are  chiefly  employed  to  form  plexuses,  or  a  net- 
work of  nervous  threads,  woven  closely  together^,  so  that  it 
cannot  be  unravelled. 


THE    NERVOUS    SYSTEM. 


315 


1 .  Hemispheres  of  the  brain  proper,  or  cerebrum. 

2.  Hemispheres  of  the  smaller  brain,  or  cerebellum. 

3.  Spinal  cord  continuous  with  the  brain,  and  the  spinal  nerves  pro- 
ceeding from  it  on  each  side. 


116  PHYSIOLOGY. 

15.  The  chief  net-works  or  ganglia  are  four  in  number. 
The  first  which  is  called  cervical,  is  formed  from  the  secondj 
third  diudi  fourth  cervical  nerves  ;  lies  on  the  side  of  the  neck 
about  its  middle  ;  and  it  gives  rise  to  four  large  nerves  which 
go  to  the  head,  neck  and  upper  part  of  the  chest.  The 
second  plexus  lies  under  the  pit  of  the  arm,  and  gives  rise  to 
eight  principal  branches  which  go  to  the  chest,  shoulder  and 
arms.  The  other  two  plexuses  lie  in  the  pelvis,  and  give  off 
branches  which  supply  the  viscera  contained  in  it,  and  also 
the  lower  extremities. 

16.  A  second  division  of  the  nervous  system,  as  I  have 
stated,  has  been  called  by  anatomists  ganglionic,  or  the  ner. 
vous  system  of  organic  life.  A  ganglion  is  a  small  grayish 
white  body,  of  a  roundish  or  oval  shape,  varying  in  size, 
irom  a  pin's  head  to  an  almond.  These  ganglions  are  chief- 
ly situated  on  the  sides  of  the  spinal  column,  throughout  its 
whole  length,  and  are  connected  by  nervous  threads,  which 
pass  from  one  to  the  other,  and  also  with  the  nerves  which 
come  out  from  the  spine.  Siv  of  these  ganglions  are  found 
in  the  head  ;  three  in  the  neck ;  twelve  in  the  dorsal  region  j 
Jive  in  the  lumbar  ;  and  three  in  the  sacral  region. 

17.  The  principal  of  the  plexuses  are  formed  by  nervous 
filaments  proceeding  from  these  ganglions.  These  are  the 
cardiac  plexus,  the  pulmonary  plexus,  and  the  great  solar 
plexus.  The  whole  ganglionic  system  of  nerves  is  called 
the  great  sympathetic  nerve.  This  is  connected  with  the  brain 
by  the  sixth  cerebral  nerve  and  a  branch  of  the  fifth.  It 
also  receives  branches  from  the  seventh,  eighth,  and  ninth, 
and  all  the  spinal  nerves,  to  the  lower  part  of  the  spine,  be- 
low which  it  terminates.  We  are  now  prepared  to  consider 
the  functions  of  the  nervous  system. 

18.  The  brain  beino-  the  centre  of  the  nervous  system,  is 
the  most  important  organ  of  the  human  body.  In  the  lowest 
order  of  animals,  we  find  but  imperfect  rudiments  of  a  ner- 
vous system  ;  but  as  w^e  ascend  in  the  scale  of  animal  exist- 
ence, we  find  it  more  and  more  developed  as  we  advance,  till 


THE    NERVOUS    SYSTEM.  117 

at  length  we  arrive  at  man,  who  possesses  it  in  its  highest 
form  of  development.  The  functions  over  which  the  brain 
presides,  are  the  sensaiionsy  the  voluntary  motions,  and  the 
intellectual  and  moral  faculties. 

19.  The  mind  itself  is  immaterial — a  principle  superadded 
to  matter  ;  but  the  brain  is  the  instrument  which  it  employs 
in  all  its  operations.  Though  it  is  not  matter,  yet  it  works 
by  means  of  matter.  In  like  manner,  the  eye  is  not  sight, 
but  the  instrument  of  sight ;  the  ear  is  not  hearing,  but  the 
organ  of  hearing  ;  so  the  brain  is  not  mind,  but  the  organ 
of  mind.  Revelation  teaches  us  all  we  know,  with  respect 
to  the  powers  and  capacities  of  mind,  when  separate  from 
the  body. 

20.  The  spinal  marrow  and  the  nerves  are  of  subordinate 
importance  ;  as  organs  of  the  nervous  system,  their  use 
seems  to  be,  to  transmit  impressions  from  the  organs  of 
sense  to  the  brain  ;  or  the  influence  of  the  brain  in  a  con- 
trary direction  to  the  muscles  which  are  employed  for 
motion. 

21.  The  first  class  of  functions  which  pertain  to  the  brain 
are  the  sensorial.  Though  the  brain  is  the  actual  seat  of 
all  impressions,  yet  the  organs  of  sense  and  the  nerves  seem 
to  be  the  immediate  seats  of  sensation.  Indeed,  no  sensation 
can  be  excited  in  any  part  or  organ,  unless  its  nervous  con- 
nection with  the  brain  be  entire.  For  example,  the  sense 
of  touch  seems  to  reside  in  the  ends  of  the  fingers,  and  that 
of  sight  in  the  eye,  yet  if  the  nerve  which  connects  these 
parts  with  the  brain  be  divided,  no  impression  is  felt,  no 
sensation  whatever  is  excited  ;  showing  conclusively  that  it 
is  the  brain  that  perceives  all  impressions  made  on  the  organs 
of  sense. 

22.  It  is  a  curious  fact  connected  with  this  subject,  that 
though  the  brain  is  the  real  seat  of  the  sensation,  yet  it  is 
always  referred  to  the  part  or  organ,  on  which  the  impression 
is  made,  so  that  there  seems  to  be  a  double  action,  viz.,  from 
the  organ  to  the  brain,  and  fi-om  the  brain  back  again  to  the 


118  PHYSIOLOGY. 

organ.  Thus  it  is  not  unusual  to  see  persons  who  have  lost 
a  limb  complaining  of  pain,  or  some  other  sensation  in  the 
part  which  has  been  cut  off,  and  thus  they  often  imagine 
that  the  limb  is  entire.  Here  the  sensation  existed  only  in 
the  mind  ;  in  the  same  manner  ghosts,  hobgoblins,  and  other 
strange  sights  are  seen  ;  but  the  sensation  is  only  in  the 
brain. 

23.  That  the  brain  is  the  real  seat  of  all  our  sensations 
may  be  proved  from  other  facts.  If  a  person  receives  a 
blow  upon  the  head  so  as  to  stun  him,  or  deprive  him  of 
consciousness,  though  the  organs  of  sensation  and  the  senses 
are  wholly  uninjured,  he  takes  no  notice  of  any  thing  ;  he 
receives  no  sensations  from  any  of  his  senses  ;  in  fact,  he  is 
said  to  be  insensible.  The  same  thing  happens  if  he  become 
stupid  by  the  use  of  alcohol,  opium,  or  any  narcotic.  If  the 
quantity  is  not  enough  to  produce  entire  torpor  of  the  brain, 
his  senses  are  impaired,  his  reason  is  gone  ;  he  i&  in  short  a 
voluntary  mad-man, 

24.  During  sleep,  the  senses  are  said  to  be  locked  up. 
But  though  the  eye  is  closed,  the  ear  is  open  ;  the  nerves  in 
which  the  sense  of  touch  resides,  are  still  spread  out  upon 
the  skin,  but  yet  no  impressions  are  felt ;  no  sensations  are 
excited  ;  no  notice  is  taken.  The  reason  is,  the  brain  is  in 
a  state  of  repose  ;  the  shi])  does  not  obey  the  rudder,  be- 
cause the  man  at  the  helm  is  asleep  ;  the  steamboat  is  not  in 
motion,  for  although  she  has  furnace,  boilors,  condensers, 
paddle-wheels,  and  all,  yet  the  steam  is  not  up  ;  so  in  sleep, 
the  organs  of  sense  are  all  sound,  yet  the  brain,  the  rudder 
of  the  mind,  the  moving  agent  of  the  animal  machine,  is 
dormant ;  the  messages  of  its  servants,  the  organs  of  sense, 
are  neither  received,  noticed,  nor  acted  upon. 

25.  There  is  another  curious  circumstance  connected 
with  the  brain  ;  it  may  be  so  much  employed  in  thought, 
or  deep  meditation,  as  not  to  notice  the  impressions  made 
on  the  senses.  In  this  case,  a  person  is  said  to  be  absent, 
minded.     Though  the  eyes  and  ears  are  open,  the  brain  is 


THE    NERVOUS    SYSTEM.  119 

too  busy  about  other  matters,  to  take  notice  of  the  impres- 
sions made  on  them  ;  accordingly,  there  are  instances  known, 
where  persons  have  walked  off  a  precipice,  or  into  the  water, 
without  noticing  the  danger  till  it  was  too  late. 

26.  Sensations,  then,  are  the  more  vivid  ;  and  the  impres- 
sions  which  they  make,  more  durable,  in  proportion  to  the 
degree  of  attention  with  which  the  mind  is  directed  towards 
them  ;  or  the  degree  of  activity  of  the  brain.  To  obtain 
ideas,  which  are  the  pictures  of  sensible  objects  painted  on 
the  brain,  we  must  therefore  endeavour  to  concentrate  the 
whole  attention  upon  the  subject  before  us,  or  the  impres- 
sions we  receive  will  be  weak  and  speedily  fade  away.  We 
see  a  great  difference  in  this  respect  in  different  persons. 
Two  individuals  will  travel  together  through  the  same  coun- 
try, and  apparently  take  the  same  degree  of  interest  in  the 
objects  which  come  under  their  notice.  Yet,  while  one  of 
these  persons  will  be  able  to  describe  minutely  every  thing 
he  has  seen,  the  other  can  give  only  a  confused  and  indistinct 
account  of  what  he  has  observed.  It  is,  therefore,  not  only 
necessary  in  the  acquisition  of  knowledge  that  objects  should 
make  an  impression  on  the  sensual  organs  ;  but  the  brain 
must  act  upon  them,  and  that  not  in  a  slight  and  careless 
manner,  but  vividly  and  energetically. 

27.  It  is  possible  even  that  sensations  may  be  excited  by 
the  action  of  the  brain  itself,  without  the  intervention  of  any 
-sensible  objects.  We  see  this  often  in  diseases  of  the  brain, 
and  especially  in  that  form  of  insanity,  called  delirium  tre. 
mens,  or  drunken  delirium.  Here,  the  wretched  victim  of 
depraved  habit  sees  serpents,  and  lizards,  and  bats,  and  all 
creeping  things,  and  devils,  flying  about ;  and  he  hears  sing- 
ing and  various  sounds,  to  which  he  listens,  and  calls  the 
attention  of  others,  and  nothing  can  break  the  spell  by  which 
-he  is  bound,  or  dispel  the  illusory  conviction,  that  what  he 
sees  and  hears  is  real  and  not  imaginary. 

28.  Such  illusory  and  false  impressions,  are  no  doubt 
sometimes  excited  in  the  minds  of  those,  who  cannot  be  said 


120  PHYSIOLOGY. 

to  labour  under  actual  disease  ;  but  their  imaginations  have 
been  excited  by  the  influence  of  fear  and  superstition,  and 
the  brain  is  accordingly  excited  to  act  in  the  same  manner 
as  it  would  by  the  actual  sight  of  some  frightful  object. 
Thus  a  post  will  appear  in  the  night,  to  be  a  robber ;  a  black 
stump  of  a  tree,  a  bear,  or  a  tomb-stone,  a  ghost ;  according 
to  the  idea  or  apprehension  at  the  time  uppermost  in  the 
mind. 

29.  But  though  the  brain  is  the  seat  of  sensation,  yet  it 
is  very  remarkable  that  it  is  not  itself  sensible.  Wounds 
in  its  substance  do  not  seem  to  excite  pain.  The  whole  of 
the  cerebrum  as  well  as  the  cerebellum  has  been  pared  away, 
and  yet  the  animal  appeared  to  suffer  no  pain  ;  but  as  soon 
as  that  portion  of  the  base  of  the  brain  which  seems  to  be 
the  commencement  of  the  spinal  marrow,  is  touched,  con- 
vulsions immediately  follow.  The  posterior  surface  of  the 
spinal  marrow  is  also  highly  sensible.  This  is  the  substance 
of  what  is  yet  known  on  the  subject  of  sensation, 

30.  Voluntary  motion,  like  sensation,  has  also  its  seat  in 
the  brain.  Though  the  muscles  are  the  instruments  of 
motion,  yet  all  their  voluntary  motions  are  performed  through 
the  influence  of  the  brain,  by  an  act  of  the  will.  If  the  brain 
is  in  a  state  of  repose  the  body  is  at  rest ;  if  the  brain  by 
an  act  of  violition  sends  a  portion  of  nervous  influence  to  a 
voluntary  muscle,  it  immediately  contracts,  and  the  limb  or 
organ  to  which  it  is  attached,  moves.  All  we  are  conscious 
of  in  this  process,  is,  the  act  of  the  will  and  the  motion,  which 
that  act  causes.  The  volition  and  the  motion  seem  to  be 
at  the  same  instant ;  at  least  there  is  no  perceptible  interval 
between  them. 

31.  But  though  the  voluntary  muscles  are  excited  to  action 
through  the  agency  of  the  brain,  yet  they  are  not  always 
under  the  control  of  the  will.  In  many  diseases  of  the 
brain  :  in  lock  jaw,  hydrophobia,  and  other  disorders  where 
the  whole  nervous  system  is  in  a  state  of  irritation,  the 
muscles  are  excited  to  violent  spasmodic  contraction,  alto- 


THE    NERVOUS    SYSTEM.  121 

gether  beyond  the  control  of  the  will.  Where  convulsions 
arise  from  sympathy,  as  in  teething,  or  irritation  of  the 
bowels,  the  painful  impression  is  transmitted  to  the  brain, 
and  hence  reflected  back  upon  the  muscles.  Thus  pricking 
the  fino;er  with  a  needle  has  thrown  a  nervous  woman  into 
spasms,  by  exciting  the  brain  to  action. 

32.  If  a  nerve  which  supplies  any  voluntary  muscle  be 
divided,  that  muscle  will  no  longer  contract.  This  proves 
that  the  influence  of  the  brain  is  necessary.  In  palsy,  there 
is  generally  some  disease  of  the  brain,  as  the  rupture  of  a 
small  blood-vessel,  or  tumour  growing  in  its  substance.  Here 
the  power  of  the  will,  or  the  faculty  of  volition  is  not  des- 
troyed ;  but  the  brain  is  unable  to  carry  into  execution  the 
command  of  the  will,  as  when  a  person  is  very  willing  to 
take  a  load  upon  his  back,  but  he  happens  not  to  have  suflS- 
cient  strength  to  carry  it. 

33.  During  sleep,  all  voluntary  motion  is  suspended,  be- 
cause the  brain  ceases  to  act.  In  those  cases  where  persons 
walk  and  talk  in  their  sleep,  the  brain  is  not  entirely  dormant. 
Some  of  the  senses  seem  to  be  awake  at  times,  while  the 
others  are  asleep.  That  is,  those  portions  of  the  brain  which 
are  excited  to  action  by  certain  nerves  of  sense,  are  awake 
and  active,  while  other  portions  are  dormant  and  at  rest. 
The  brain  needs  repose  and  relaxation,  as  much  as  the 
muscles.  Periodical  cessation  of  effort  is  necessary  to  both, 
in  order  to  a  vigorous  performance  of  their  respective  func- 
tions. 


Questions. — What  functions  belong  to  the  nervous  system  ?  What 
cloes  it  embrace  ?  How  many  departments  ?  What  offices  does  each 
perform  ?  What  marks  characterize  each  ?  When  their  functions  are 
interrupted,  what  happens  ?  From  what  portion  of  the  spinal  mar- 
row do  the  nerves  of  motion  arise  ? — the  nerves  of  sensation  ?  Des- 
cribe  the  brain  ; — its  divisions ; — its  membranes  ; — dura  mater  ; — pice 
mater ;  What  are  the  convolutions  of  the  brain  ?  How  do  the  cine- 
ritious  and  medullary  portions  differ  from  each  other  ?  Which  is  ex 
terior  ?    How  many  cavities  in  the  brain  ?    What  are  they  called  ? 

11 


122  PHYSIOLOGY. 

Describe  the  cerebellum, — the  spinal  marrow.  How  many  pairs  of 
nerves  are  there  ?  How  many  nerves  arise  from  the  cerebrum  ? — from 
the  pons  varolii  ? — from  the  spinal  marrow  ? — from  the  medulla  oblon- 
gata ?  How  many  principal  ganglia  or  net-works  of  nerves  ? — their 
situation  ?  What  is  a  ganglion  ?  What  are  the  principal  ganglions 
of  the  nervous  system  of  organic  life  ?  What  is  the  sympathetic  nerve  ? 
— where  situated  ?  What  is  the  most  important  organ  of  the  body  ? 
What  is  said  of  the  brain  in  the  lower  animals  ?  Over  what  functions 
does  the  brain  preside  ?  Is  it  immaterial  ?  What  is  the  first  class 
of  functions  over  which  it  presides  ?  What  is  understood  by  sensorial 
functions  ?  What  becomes  of  the  senses  during  sleep? — during  absent- 
mindedness  ?  What  are  ideas  ?  Is  attention  necessary  in  order  to  im- 
press sensations  durably  on  the  mind  ?  May  sensations  be  excited 
without  the  intervention  of  sensible  objects  ?  In  what  disease  does  this 
happen  ?  Is  the  brain  itself  sensible  ?  Where  is  the  seat  of  voluntary 
motion  ?  How  is  it  performed  ?  What  is  volition  ?  Are  motions 
always  under  the  control  of  the  will  ?  In  what  diseases  is  this  not  the 
case?  What  effect  has  the  division  of  a  nerve?  What  happens  in 
palsy  ?     Why  is  voluntary  motion  suspended  during  sleep  ? 


CHAPTER  X, 

INTELLECTUAL  AND  MORAL  FACULTIES. 

1.  The  great  superiority  of  the  intellectual  faculties  of 
man  over  those  of  other  animals,  has  led  to  a  diligent  exami- 
nation, whether  there  be  any  thing  in  his  anatomical  struc- 
ture which  would  seem  to  account  for  this  superiority. 
Aristotle  noticed  the  great  size  of  the  human  brain  compared 
with  that  of  other  animals,  and  laid  it  down  as  a  general 
principle,  that  the  faculties  referred  to  this  organ  were  in 
proportion  to  its  size,  compared  with  that  of  the  whole  body. 
Though  this  rule  will  hold  true  in  relation  to  some  of  the  do- 
mestic animals,  yet- it  does  not  in  relation  to  many  others, 
for  accurate  researches  have  shown  that  while  in  man  the 
ratio  of  the  weight  of  the  brain  to  that  of  the  whole  body  is 
as  1  to  28,  in  the  dog,  it  is  as  1  to  160,  in  the  horse,  as  1  to 
400,  in  the  elephant,  1  to  500,  in  the  canary  bird,  1  to  14, 
and  in  one  species  of  ape,  1  to  11. 

2.  It  is  now  generally  admitted  by  physiologists,  that  the 
perfection  of  the  sensitive  functions  does  not  depend  on  the 
absolute  size  of  the  brain,  nor  on  its  proportion  to  the  body 
at  large,  but  upon  the  proportion  between  the  size  of  the 
brain,  and  the  aggregate  bulk  of  the  nerves  that  proceed 
from  it  ;  in  other  words,  between  the  sensorial  and  nervous 
organs.  For  example,  the  absolute  size  of  the  brain  of  the 
horse  is  only  about  half  the  size  of  the  human  brain,  while 
the  mass  of  the  nerves  of  the  horse  at  their  origin  is  no  less 
than  ten  times  larger  than  that  of  man.  Extensive  observa- 
tions prove  that  though  most  of  the  inferior  animals  have  larger 
nerves,  and  possess  some  of  the  nervous  functions  in  a  much 
more  acute  state  than  man,  yet  man  decidedly  exceeds  them 
all  in  the  comparative  size  of  the  brain,  and  in  the  perfection 
of  his  intellectual  faculties. 


124  PHYSIOLOGY. 

3.  The  brain  then,  is  the  organ  of  the  intellectual  and 
moral  faculties,  the  material  instrument  of  the  mind.  This 
is  proved  not  only  by  comparative  anatomy,  and  experiments 
on  animals,  but  by  the  history  of  injuries  of  the  brain,  com- 
pared with  those  af  other  organs.  We  know  that  if  the 
nerves  supplying  any  limb  are  severed,  the  will  has  no  longer 
any  influence  over  it ;  it  is  to  all  useful  purposes  a  dead  por- 
tion of  matter.  The  same  is  true  of  the  spinal  marrow.  If 
this  be  compressed  by  fracture  or  dislocation  of  the  spine, 
the  whole  body  below  that  point,  is  deprived  both  of  sensa- 
tion and  motion,  but  the  mind  loses  none  of  its  powers  any 
more  than  if  a  limb  had  been  amputated. 

4.  If  the  brain  is  not  the  seat  of  the  intellectual  faculties, 
neither  are  any  of  the  other  organs  of  the  body.  The 
lungs,  the  liver,  the  spleen,  the  intestines,  or  the  kidneys, 
may  be  affected  with  gangrene,  and  still  the  mind  remains 
clear ;  though  from  sympathy,  inflammation  of  any  organ 
may  cause  delirium,  or  other  mental  aflections.  Neither 
is  the  heart  the  seat  of  the  mind  ;  for  cronic  disease  of  that 
organ,  does  not  impair  the  mental  faculties.  Besides  the 
functions  of  all  these  organs  are  known  and  cannot  be  mis- 
taken. If  the  brain  is  not  the  seat  of  the  inteMectual  facul- 
ties, they  cannot  be  said  to  have  any  seat  in  the  body. 

5^  But  the  effects  of  injuries  of  the  brain  are  very  diffe- 
rent, for  every  cause  which  disturbs  its  action  suddenly  op 
slowly,  affects  at  the  same  time  the  mind.  Inflammation  of 
the  brain  is  always  attended  with  delirium,  or  stupor  ;  pres- 
sure on  it,  whether  produced  by  depressed  bone,  foreign 
bodies,  a  tumour,  serum,  blood  or  pus,  always  gives  rise  to 
similar  symptoms,  and  often  destroy  both  sensation  and 
motion.  In  cases  of  apoplexy,  where  a  person  falls  in  a  fit, 
and  becomes  insensible,  we  find  pressure  on  the  brain  from 
effusion  of  blood  or  serum.  In  cases  of  lunatics,  we  find  in 
nearly  all  cronic  cases,  structural  changes  in  the  brain  ;  but 
if  the  case  be  recent,  these  changes  though  they  probably 
exist,  yet  may  escape  our  imperfect  means  of  investigation. 
Alcohol,  opium,  and  other  narcotics  affect  the  mind  and  the 


INTELLECTUAL    AND    MORAL    FACULTIES.  125 

Rerves  through  their  influence  upon  the  brain.  Whenever 
in  fact,  we  see  a  person  become  stupid  and  insensible,  we 
may  be  certain  that  the  brain  has  suffered  some  physical 
change ;  and  where  in  cases  of  sickness,  we  see  the  mental 
faculties  unimpaired  to  the  last,  we  may  be  equally  sure,  that 
the  brain  is  not  affected, 

6.  The  following  facts  also  show  that  the  brain  is  the  or- 
gan of  the  mind.  A  man  received  a  blow  on  his  head,  and 
immediately  lost  his  mental  faculties,  and  his  bodily  power. 
His  appetite  and  digestion  were  good  ;  the  blood  circulated 
freely  ;  and  his  breathing  and  pulse  were  natural.  He  con- 
tinued in  this  state  more  than  a  year,  when  a  surgeon  raised 
up  a  piece  of  bone  which  had  been  driven  in  upon  the  brain. 
His  reason  was  immediately  restored  ;  the  next  day  he 
spoke,  and  in  a  short  time  he  recovered  entirely ;  but  he 
could  recollect  nothing  of  what  had  happened  since  the  acci- 
dent. Not  long  since  a  beggar  exhibited  himself  in  Paris, 
who  had  lost  a  portion  of  his  skull ;  his  brain  was  only  cov- 
ered by  the  skin  and  membranes.  For  a  trifling  sum  he 
would  allow  any  one  to  press  on  this  exposed  part.  As  soon 
as  any  pressure  was  made  he  became  wholly  unconscious ; 
but  his  intellect  was  immediately  restored  when  the  pressure 
was  taken  off. 

7.  It  has  been  objected  to  the  brain's  being  considered  the 
seat  of  the  mind,  that  in  some  cases,  considerable  disease 
has  been  found  affecting  an  entire  hemisphere  without  the 
mental  faculties  having  suffered  ;  but  experiments  on  animals 
show  that  a  sudden  lesion  of  one  hemisphere  only,  does  not 
immediately  produce  complete  stupor,  and  that  this  effect 
does  not  follow  until  both  are  removed  ;  so  that  it  appears 
that  one  hemisphere  aids  the  other,  and  compensates  for  its 
inaction  in  the  operations  of  the  mind. 

8.  But  though  it  is  almost  universally  admitted,  that  the 
brain  is  the  seat  of  the  higher  intellectual  faculties,  yet  some 
physiologists,  like  Bichat,  contend  that  the  passions  are 
seated  in  the  thoracic  and  abdominal  viscera.  It  is,  however, 

11* 


126  PHYSIOLOGY. 

to  be  remarked,  that  the  passions,  by  means  of  the  change 
which  takes  place  in  the  brain,  affect  the  whole  nervous  sys. 
tem.     We  find,  for  example  in  nervous  females,  that  the  ex- 
citing passions  give  rise  to  spasmodic  action  of  certain  mus- 
cles, especially  those  supplied  by  nerves  belonging  to  the 
respiratory  system  ;  hence  the  crying,  sobbing,  sighing,  and 
the  spasmodic  distortion  of  the  features.     In  the  depressing 
passions,  such  as  fear  and  terror,  the  muscles  of  the  body  lose 
their  tone,  because  the  supply  of  nervous  influence  from  the 
brain  is  cut  off;  the  limbs  are  not  able  to  support  the  body  ; 
the  features  lose  their  expression  ;  and  the  loss  of  power  may 
be  so  great  as  to  cause  complete  paralysis  of  the  whole  body. 
9.  In  like  manner  is  the  heart  affected  by  the  exciting  and 
depressing  passions.     It  throbs  irregularly  under  the  influ- 
ence of  fear  and  terror ;  it  beats  high  and  strong  under  the 
influence  of  joy ;  while   its  action  is  weakened  under  the 
operation  of  grief  and  care ;  in  short,  it  is  affected  in  a 
greater  or  less  degree  by  every  emotion  which  agitates  the 
human  breast.     But  this  no  more  proves  that  the  passioua 
are  seated  in  the  heart,  than  that  they  are  seated  in  the  eye, 
because  grief  brings  tears  into  that  organ.     Neither  has  the 
liver,  as  the  ancients  believed,  any  relation  to  the  passions  of 
rage  and  vexation,  although  a  fit  of  jaundice,  may,  in  some 
persons  labouring  under  a  disease  of  this  organ,  follow  a 
paroxysm  of  these  passions.     In  other  individuals,  a  fi'^  of 
dyspepsia  may  follow  as  a  consequence  of  the  same  emotions  ; 
or  any  other  organ,  may  suffer,  according  as  it  is   predis- 
posed by  debility,  disease,  or  other  causes.     Such  phenome- 
na only  prove  that  the  whole  body  is  bound  up  in  one  indis- 
soluble bond  of  sympathy,  or  as  St.  Paul  expresses  it,  "  God 
hath  tempered  the  body   together,  that   there  should  be  no 
schism  in  the  body,  but  that  the  members  should  have  the 
same  care  one  for  another  ;  so  that,  whether  one  member  suf- 
fer, all  the  members  suffer  with  it,  or  one  member  be  honored, 
all  the  members  rejoice  with  it." 

10.  The  brain,  like  all  the  other  organs  of  the  body,  in- 


INTELLECTUAL    AND    MORAL    FACULTIES.  127 

creases  in  volume,  by  the  exercise  of  its  functions.  When 
the  mind  is  properly  cultivated,  the  brain  attains  its  full 
growth  and  development ;  and  where  suitable  opportunities 
of  education  have  been  enjoyed,  the  intellectual  powers  are 
generally  proportioned  to  the  size  of  this  organ.  Majendi 
says,  "  The  volume  of  the  brain  is  generally  in  direct  pro- 
portion to  the  capacity  of  the  mind."  This  was  also  be- 
lieved by  the  ancient  Greeks  ;  for  their  statuaries,  or  workers 
in  marble,  made  the  heads  of  their  Apollo,  and  other  intel- 
lectual gods  and  heroes,  much  larger  than  the  heads  of  their 
Hercules,  and  other  heroes,  who  were  remarkable  only  for 
their  great  physical  strength.  The  heads  of  idiots  are  known 
to  be  extremely  small ;  some,  indeed,  are  not  more  than  one- 
fifth  the  average  size. 

11.  That  the  brain  is  constructed  with  evident  design, 
and  is  composed  of  a  number  of  curiously  wrought  parts,  all 
physiologists  admit ;  yet  they  have  not  been  able  thoroughly 
to  penetrate  the  intention  with  which  they  are  formed,  or  to 
agree  with  respect  to  the  particular  functions  which  each 
part  performs.  It  is,  however,  pretty  well  ascertained,  that 
the  hemispheres  of  the  large  brain,  or  cerebral  lobes,  are  the 
instruments  by  which  the  intellectual  operations  are  carried 
on  ;  in  other  words,  are  the  seats  of  the  faculties  of  thinking, 
memory^  and  the  will ;  while  the  central  parts,  such  as  the 
optic  lobes,  ft,nd  the  medulla  oblongata,  are  principally  con- 
cerned in  sensation  ;  and  that  the  cerebellum,  or  tittle  brain, 
is  the  chief  sensorial  agent  in  voluntary  motion,  and  the  seat 
of  the  animal,  or  lower  propensities. 

12.  Many  cruel  experiments  have  been  made  on  living 
animals,  to  determine  the  exact  functions  of  particular  parts 
of  the  brain  ;  but  so  much  violence  is  done  in  these  experi- 
ments, that  but  little  dependence  can  be  placed  on  them. 
Many  attempts  have  been  made  to  determine  the  exact  place 
in  the  brain  where  perception  resides,  but  all  such  attempts 
have  been  fruitless.  That  it  is  placed  in  the  base  of  the 
brain,  or  the  medulla  oblongata,  is  very  probable,  as  most  of 


1 28  PHYSIOLOGY, 

the  nerves  of  sense  terminate  in  that  part ;  but  it  is  difficult 
to  prove  this  by  actual  experiment, 

13.  The  brain,  like  all  the  organs  of  the  senses,  is  double ; 
the  one  side,  as  in  the  eyes,  ears,  and  limbs,  being  exactly 
similar  to  the  other  ;  so  that  it  may  be  said,  that  we  have 
tivo  brains  as  well  as  two  optic  nerves,  and  two  eyes.  As  the 
structure  of  the  brain  is  Jibrous,  in  order  that  the  two  sets 
of  fibres  may  co-operate,  and  constitute  a  single  organ,  they 
pass  obliquely  across  from  one  side  of  the  brain  to  the  other, 
and  these  bridges  constitute  what  are  called  the  commissures 
of  the  brain.  It  follows  from  this,  that  if  the  right  side  of 
the  brain  receives  an  injury,  it  will  be  felt  on  the  opposite 
side  of  the  body.     The  following  case  proves  this. 

14.  A  piece  of  wire  pierced  the  brain  of  a  boy  just  over 
the  right  eye  ;  he  immediately  lost  all  motion  in  the  left  arm 
and  leg,  although  his  sense  of  feeling  was  as  perfect  as  ever. 
There  are  many  such  cases  on  record,  whi-ch  conclusively 
show  that  the  right  side  of  the  brain  furnishes  nerves  of 
sense  and  motion  to  the  left  side  of  the  body  ;  and  the  left 
side  of  the  brain  to  the  right  side  of  the  body.  If,  then,  a 
portion  of  brain  is  lost  by  a  wound,  on  one  side  of  the  head 
only,  as  has  often  happened,  and  the  intellect  does  not  suffer ; 
as  the  brain  is  a  double  organ,  it  does  not  prove,  that  it  is 
not  the  seat  of  the  mental  faculties. 

15.  The  office  of  the  cerebellum  is  supposed  by  many  to 
be,  to  regulate  and  combine  different  motions.  For  example, 
if  the  cerebellum  be  wounded,  the  animal  cannot  walk  with- 
out staggering,  and  there  will  be  a  particular  weakness  on 
that  side  which  is  wounded.  When  a  person  is  intoxicated, 
his  inability  of  walking  in  a  straight  course,  is  supposed  to 
be  owing  to  the  influence  of  the  alcohol  on  the  cerebellum. 
In  experiments,  where  the  cerebellum  has  been  wounded  or 
divided,  the  animal  has  rolled  over  and  over,  or  whirled  round 
and  round  ;  the  eyes  squinted  ;  and  all  power  of  regulating 
its  motions  seems  to  have  been  lost. 

16.  Though  man   is  infinitely  exalted  above  the  brute 


INTELLECTUAL  AND  MORAL  FACULTIES.     129 

creation,  by  the  endowments  of  reason  and  a  moral  sense, 
yet  many  of  the  inferior  animals  excel  him  in  the  perfection 
of  subordinate  powers.  In  strength  and  swiftness,  he  is  sur- 
passed by  many  of  the  quadrupeds  ;  in  powers  of  vision,  the 
eagle  and  other  birds  excel  him  ;  in  acuteness  of  hearing, 
taste,  and  smell,  a  large  number  of  animals  are  superior  to 
him.  Man  is  indeed  a  stranger  to  those  delicate  percep- 
tions, which  teach  the  lower  animals  to  seek  the  food  which 
is  salutary,  and  avoid  that  which  is  injurious,  and  has  to 
depend  upon  a  painful  and  hazardous  experience  for  that 
knowledge  which  the  brutes  possess  by  instinct. 

17.  "But  he  has  gifts  of  infinitely  higher  value.  In  the 
fidelity  and  tenacity  with  which  impressions  are  retained  in 
his  memory  ;  in  the  facility  and  strength  with  which  they 
are  associated  ;  in  grasp  of  comprehension,  in  strength  of 
reasoning,  in  capacity  of  progressive  improvement,  he  leaves 
all  other  animals  at  an  immeasurable  distance  behind.  He 
alone  enjoys  in  perfection  the  gift  of  utterance  ;  he  alone  is 
able  to  clothe  his  thoughts  in  words  ;  in  him  alone  do  we 
find  implanted  the  desire  of  examining  every  department  of 
nature,  and  the  power  of  extending  his  views  beyond  the 
confines  of  this  globe." 

18.  "  On  him  alone  have  the  high  privileges  been  bestow- 
ed of  recognising  and  adoring  the  Power,  the  Wisdom,  and 
the  Goodness  of  the  Author  of  the  universe,  from  whom  his 
being  has  emanated,  to  whom  he  owes  all  the  blessings  which 
attend  it,  and  to  whom  he  has  been  taught  to  look  forward 
to  brighter  skies,  and  to  purer  and  more  exalted  conditions 
of  existence." 

19.  Phrenology. — The  actual  meaning  of  the  term  Phren- 
ology,  is  "  a  discourse  about  the  mind,"  or,  "  the  doctrine  of 
the  mind."  It  professes  indeed  to  be  a  system  of  Mental 
Philosophy,  and  as  it  is  pretends  to  be  founded  in  nature  and 
supported  by  facts,  it  certainly  is  not  beneath  the  attention 
of  the  candid  inquirer  after  truth. 


130  PHYSIOLOGY. 

20.  The  chief  doctrines  which  Phrenology  claims  to  have 
established  are  the  following  : — ■• 

1.  That  the  moral  and  the  intellectual  faculties  are  in- 
nate. 

2.  That  their  exercise,  or  manifestation,  depends  on  organ- 
ization. 

3.  That  the  brain  is  the  organ  of  all  the  propensities,  sen- 
timents, and  faculties, 

4.  That  the  brain  is  composed  of  as  many  particular 
organs  as  there  are  propensities,  sentiments,  and  faculties, 
which  differ  essentially  from  each  other.  These  four  pro- 
positions may  be  said  to  constitute  the  phrenological  doc- 
trine, and  they  are  sustained  by  such  numerous  experiments, 
observations,  and  facts,  that  a  large  proportion  of  enlighten- 
ed physiologists  of  the  present  day  acquiesce  in  their  cor- 
rectness. 

21.  Another  and  a  different  proposition,  however,  and  one 
which,  by  many,  is  erroneously  supposed,  alone,  to  constitute 
Phrenology,  is,  that  we  are  able  to  recognise  on  the  exterior 
of  the  skull,  the  seats  of  the  particular  organs,  or  intellectual 
and  moral  faculties,  and  thus  determine  the  character  of  in- 
dividuals. This  proposition  has  not  received  that  general 
concurrence  of  Physiologists,  in  its  support,  which  has  at- 
tended the  former  ;  but  there  are  so  many  zealous  and  able 
inquirei's  now  in  the  field,  and  such  is  the  ardour  in  pursuit 
of  knowledge,  connected  with  this  subject,  that  a  few  years 
at  farthest,  probably,  will  suffice  to  overthrow  or  establish  it. 

22.  I  have  already  mentioned  some  facts,  to  prove  that 
the  brain  is  the  organ  of  the  mind,  and  that  the  condition 
of  that  organ  influences  the  mind  ;  let  us  now  inquire  whether 
the  mind,  in  every  act,  employs  the  whole  brain  as  one  organ, 
or  whether  separate  faculties  of  the  mind  are  connected  with 
distinct  portions  of  the  brain  as  their  respective  organs  ? 

23.  It  is  a  well  established  fact  in  Physiology,  that  differ- 
ent functions  are  never  performed  by  the  same  organ,  but 
that  each  function  has  an  organ  for  itself.     Thus  the  eyes 


INTELLECTUAL  AND  MORAL  FACULTIES.     131 

see,  the  ears  hear,  the  tongue  tastes,  the  nose  smells,  the 
stomach  digests  food,  the  heart  circulates  the  blood,  the  liver 
secretes  bile,  &c.  Even  where  the  function  is  compound, 
as  in  the  tongue,  where  a  feeling,  taste,  and  motion  are  all 
combined,  we  find  a  separate  nerve  for  each  function,  and 
the  same  occurs  in  every  part  of  the  body.  Now,  as  no 
nerve  performs  two  functions,  we  may,  reasoning  from 
analogy,  conclude,  that  it  is  so  in  the  brain  ;  different  sen- 
timen'ts,  different  faculties,  and  different  propensities,  require 
for  their  manifestation  different  organs  or  portions  of  cerebral 

matter. 

24.  Again,  the  external  senses  have  for  their  exercise,  not 
only  separate  and  external  organs,  but  also  as  many  separate 
internal  organs.  Hearing,  seeing,  smelling,  &c.,  require 
different  portions  of  cerebral  substance  for  their  exercise  ; 
may  we  not  then  from  analogy,  be  justified  in  the  conclusion, 
that  there  are  as  many  cerebral,  or  nervous  systems,  or 
organs,  as  there  are  special  internal  senses,  and  particular 
intellectual  and  moral  faculties?  The  legitimate  inference 
then  is,  that  each  faculty  does  possess  in  the  brain  a  nervous 
organ  appropriated  to  its  production,  the  same  as  each  of  the 
senses  has  its  particular  nervous  organ. 

25.  The  structure  of  the  brain  is  not  homogeneous,  but 
differs  greatly  in  different  parts,  both  in  composition,  form, 
colour,  consistence,  and  arrangement.  But  what  object 
could  there  be  in  all  this  variety,  if  the  brain  acted  as  a 
whole,  and  there  was  but  a  single  intellectual  principle  or 
.faculty  ?  A  difference  of  structure  shows  that  there  must  be 
a  difference  of  function,  and  as  the  brain  has  been  proved  to 

.  be  the  organ  of  the  mind,  it  follows  that  different  portions  or 
organs  of  the  brain  must  be  employed  by  the  intellectual  and 
moral  faculties. 

26.  The  faculties  do  not  all  appear  at  once,  nor  do  they  fail 
at  once,  but  they  appear  in  succession,  and  as  a  general  rule, 
the  reflecting  or  reasoning  faculties  are  the  latest  in  arriving 
at  perfection.     So  also  the  organization  of  the  brain  is  un- 


132  PHYSIOLOGY. 

folded  m  a  slow  and  gradual  manner,  and  the  intellectual  fac- 
ulties appear  in  succession  only  as  the  structure  is  perfected. 
For  example,  in  infancy,  the  cerebellum  forms  one  fifteenth 
of  the  encephalic  mass  ;  in  adult  age  about  one  sixth.  In 
childhood  the  middle  parts  of  the  forehead  preponderate  ;  in 
later  life,  the  upper  lateral  regions  are  more  prominent, 
which  facts  are  also  in  accordance  with  the  periods  of  unfold- 
ing the  knowing  and  reasoning  faculties. 

27.  Genius  is  almost  always  partial ;  that  is,  men  gene- 
rally have  a  taste  or  faculty,  for  one  particular  pursuit,  or 
study,  in  which  alone  they  have  the  power  of  excelling.  One 
has  a  talent  for  poetry,  another  for  mechanics,  another  for 
drawing,  music,  or  mathematics,  and  that  is  often  developed 
at  a  very  early  age,  and  without  the  advantages  of  educa- 
tion, or  particular  instruction,  and  these  persons  may,  in  all 
other  pursuits,  be  below  mediocrity.  Indeed,  nothing  is 
more  common  than  to  see  in  the  same  individuals  some  fac- 
ulties acute  and  powerful,  while  others  are  feeble  and  defec- 
tive; having  an  extraordinary  memory  for  dates,  words, 
places,  &;c.,  while  as  to  other  things  it  is  deficient.  Such 
facts  are  not  easily  explained  on  the  scheme  of  a  single  in- 
tellectual faculty,  and  a  single  organ  devoted  to  its  exercise. 

28.  It  is  an  observation  of  common  notoriety,  that  when 
the  mind  is  fatigued  with  one  kind  of  occupation  or  study,  it 
can  engage,  with  vigour,  in  one  of  a  different  kind,  requiring 
the  exercise  of  different  faculties  ;  and  thus,  instead  of  fa- 
tiguing, actually  acts  as  a  restorative.  Could  this  happen, 
unless  there  were  a  plurality  of  faculties  and  organs  of  the 
intellect  ? 

29.  The  phenomena  of  partial  idiocy  and  partial  insanity 
are  at  variance  with  the  doctrine  of  a  single  organ  of  mind. 
We  often  see  persons  in  a  state  of  monomania,  that  is,  they 
are  rational  enough  on  all  subjects  but  one ;  but  in  relation 
to  that,  they  are  entirely  mad.  Now,  if  the  brain  be  suffi- 
ciently sound  to  manifest  all  the  other  faculties  in  their  per- 
fect state,  why  is  it  not  also  able  to  manifest  this  ? 


INTELLECTUAL  AND  MORAL  FACULTIES.     133 

30.  Numerous  cases  are  contained  in  medical  works 
where  a  wound  of  the  brain  was  succeeded  by  the  loss  of  a 
single  faculty,  and  sometimes  by  exciting  inflammation,  be- 
stowed unwonted  energy  on  a  single  faculty.  Larrey,  in  his 
surgical  memoirs,  mentions  several  cases  of  wounds  made  by 
bayonets  and  swords  penetrating  the  brain  through  the  orbit 
of  the  eye,  which  entailed  the  loss  of  memory  for  names,  but 
not  of  things,  &c. 

31.  Such  are  a  few  of  the  arguments  adduced  by  writers 
on  this  subject,  to  prove  that  the  brain  is  not  only  the  organ 
of  the  mind,  but  an  apparatus,  a  congeries  of  organs,  each  of 
which  is  the  seat  of  a  particular  faculty,  the  organ  of  a  par- 
ticular  function.  The  evidence  to  most  minds  will  appear 
satisfactory  and  conclusive  on  this  point,  though  other  facts 
and  more  extended  investigations  are  needed  to  place  the 
science  on  a  permanent  foundation. 


Questions. ^What  was  Aristotle's  theory  in  relation  to  the  size  of  the 

brain  ?  How  does  its  size  compare  with  that  of  the  body  in  man  ? 
in  the  dog,  the  horse  ?  the  elephant  ?  the  canary  bird  ?  the  ape  ?  What 
is  now  the  received  doctrine  in  relation  to  the  size  of  the  brain  ?  How 
is  it  proved  that  the  brain  is  the  organ  of  the  intellectual  and  moral 
powers  ?  How  do  you  prove  that  no  other  organ  than  the  brain  can  be 
the  seat  of  the  mind  ?  How  does  inflammation  or  injuries  of  the  brain 
affect  the  mind  ?  What  cases  prove  this  connection  ?  What  objec- 
tions have  been  raised  to  the  brain  being  the  organ  of  the  mind  ?  What 
is  said  of  the  passions  being  situated  in  the  viscera  of  the  chest  or  abdo- 
men ?  Does  the  affection  of  the  heart  by  passion  prove  that  it  is  the 
seat  of  th«  mind  ?  Why  not  ?  Does  the  brain  increase  in  size  by  ex- 
ercise ?  What  was  the  opinion  of  the  ancient  Greeks  on  this  subject  ? 
W^hat  is  said  of  the  functions  of  particular  portions  of  the  brain  ?  Is 
much  dependance  to  be  placed  on  the  experiments  made  on  animals? 
Where  is  it  supposed  perception  resides  ?  What  are  the  commisseurs 
of  the  brain  ?  When  the  brain  is  injured  on  the  right  side,  which  side 
of  the  body  is  affected  ?  What  accident  proves  that  the  opposite  side  is 
affected  ?  What  is  the  office  of  the  cerebellum  ?  What  effect  do  we 
see  in  animals  when  they  have  been  wounded  ?  Is  man  excelled  by  ani. 
mals  in  the  perfection  of  the  senses  ?  In  what  respect  does  he  excel  all  ani- 

12 


134  PHYSIOLOGY. 

mals?  What  is  Phrenology  ?  What  are  its  chief  doctrines?  What 
is  said  of  locating  the  organs  on  the  exterior  of  the  skull  ?  What  facts 
show  that  the  brain  does  not  act  as  as  a  whole  in  the  intellectual  opera- 
tions? Have  the  external  senses  separate  internal  organs?  What 
may  we  infer  from  this  ?  Is  the  structure  of  the  brain  homogeneous  ? 
Do  the  faculties  all  appear  at  the  same  time  ?  Is  genius  generally 
partial?  When  the  mind  is  fatigued,  what  effect  is  experienced  by 
turning  the  attention  to  a  different  subject  ?  What  is  monomania  ? 
What  do  we  infer  from  its  existence  ?  What  is  the  general  conclusion 
in  relation  to  the  chief  doctrines  of  Phrenology  ? 


CHAPTER  XL 

THE  SPINAL  MARROW  AND  ITS  FUNCTIONS. 

1.  We  have  seen,  that  of  all  animals,  the  brain  of  man 
"has  the  greatest  development,  in  proportion  to  the  spinal 
marrow  and  nerves  ;  if  we  descend  to  the  lower  animals, 
«uch  as  reptiles  and  fishes,  we  shall  find  that  the  brain  pre- 
sents merely  a  delicate,  anterior  termination  of  the  spinal 
cord,  not  much  larger  in  diameter  than  the  cord  itself.  In 
these  animals,  we  find  the  instincts  very  limited,  and  the 
displays  of  sagacity  extremely  obscure  ;  while  they  possess 
great  tenacity  of  life.  Frogs,  for  example,  continue  to  jump 
about  for  many  hours  after  their  heart  has  been  torn  out ; 
and  the  heart  of  the  shark  will  palpitate  as  long  after  it  has 
been  removed  from  the  body.  Turtles  have  been  known  to 
live  for  months  after  the  whole  brain  has  been  scooped  out. 
These  facts  prove,  that  such  an  imperfect  development  of 
the  cerebral  mass,  leaves  the  diflTerent  systems  of  organs  less 
intimately  connected  and  more  independent  of  each  other. 

2.  If  we  descend  still  lower  in  the  scale  of  invertebrate 
animals,  we  shall  find  the  different  parts  still  more  independ- 
ent of  each  other  ;  for  if  we  divide  their  bodies,  so  that  each 
part  will  possess  a  nervous  ganglion,  it  will  become  a  separ- 
ate individual,  and  exercise  all  the  functions  performed  by 
tlie  entire  animal  ;  and  if  we  descend  to  zoophytes,  we  find 
that  in  cutting  them  into  threads,  however  minute,  each 
piece  will  retain  life  and  continue  to  grow. 

3.  Medulla  ohlongaia. — There  is  no  distinct  line  of  demar- 
cation between  the  medulla  oblongata  and  the  spinal  cord. 
For  this  reason,  they  are  considered  and  described  as  one 
organ.  The  medulla  oblongata,  however,  consisting  of  six 
columns,  gives  rise  to  several  nerves  of  distinct  function,  and 


136  PHYSIOLOGY. 

^is  supposed  to  be  the  point  at  which  excitement  to  motion 
commences  and  sensation  terminates,  and  to  possess  the 
power  of  originating  motion  in  itself.  Mr.  Mayo  infers 
this,  from  the  fact  that  the  bi'ain  proper,  the  optic  tuhercles, 
and  even  the  cerebellum  may  be  removed  by  successive  por- 
tions, and  still  the  animal  live,  and  exhibit  feeling  and  in- 
stinct ;  but  if  the  medulla  oblongata  be  removed,  all  con- 
sciousness is  immediately  destroyed.  Other  physiologists 
say,  that  it  is  the  hemispheres  of  the  cerebrum  that  take 
cognizance  of  sensation,  and  the  source  from  whence  volition 
proceeds  ;  and  that  though  they  may  be  removed,  layer 
after  layer,  without  pain,  yet  by  so  doing,  the  senses  are 
destroyed,  memory  and  intelligence  abolished,  and  the  animal 
reduced  to  an  automaton,  destitute  of  design,  apprehension, 
and  judgment.  As  all  the  nerves  which  supply  the  larynx, 
lungs,  heart,  stomach,  and  external  muscles  of  respiration 
originate  from  it,  its  removal  must  instantly  destroy  life. 

4.  The  spinal  cord  passess  down  through  the  foramen 
magnum,  or  great  hole  of  the  skull,  and  the  canal  of  the  ver- 
tebra, till  it  reaches  the  second  vertebra  of  the  loins,  where 
it  generally  terminates  in  a  tapering  point.  Besides  the 
bony  case  in  which  it  is  lodged,  the  cord  is  enclosed  by  a 
prolongation  of  the  dura  mater,  which,  however,  does  not 
adhere  immediately  to  the  bone,  as  it  does  in  the  skull.  It 
also  is  supplied  with  extensions  of  the  arachnoid  and  pia 
mater  ;  between  which,  there  is  usually  a  quantity  of  serous 
fluid,  varying  from  two  to  six  ounces,  which  seems  to  impart 
a  certain  degree  of  support  by  its  pressure  and  obviates  the 
effects  of  concussion. 

5.  The  general  form  of  the  spinal  cord  is  cylindrical, 
though  somewhat  flattened,  from  its  transverse  diameter 
being  the  greatest.  Its  thickness,  however,  is  not  uniform, 
as  it  bulges  out  at  the  lower  part  of  the  neck,  where  the 
nerves  go  off  to  the  arms,  and  also  at  the  lower  part  of  the 
back,  from  whence  spring  the  nerves  of  the  legs.  It  is  com- 
posed of  grey  and  white,  or  cineritious  and  medullary  mat- 


THE  SPINAL  MARROW  AND  ITS   FUNCTIONS. 


137 


ter,  like  the  brain  ;  the  situation  of  the  two  is,  however, 
reversed  ;  the  medullary  matter  being  disposed  in  a  thin 
layer  upon  the  surface,  while  the  grey  portions  occupies  the 
centre.  We,  however,  find  the  same  arrangement  in  the 
medulla  oblongata,  and  the  central  parts  of  the  cerebrum 
and  cerebellum.  The  chord,  as  I  have  already  mention- 
ed, is  divided  into  two  lateral  halves  by  a  groove  in  front 
and  a  similar  groove  behind.  Besides  this,  there  are  on 
each  side  two  lateral  grooves  faintly  marked,  from  which 
the  anterior  and  posterior  nerves  have  their  origin,  so  that 
in  fact,  the  cord  consists  of  four  columns  ;  from  the  two 
anterior  of  which,  the  nerves  of  motion  spring,  and  from  the 
two  posterior  those  of  sensation. 

a 


a,  Spinal  marrow. 
6,  Fibres  of  sensation. 
c.  Fibres  of  motion. 
e,  Nerve. 

6.  There  are  thirty  pairs  of  nerves  that  spring  from  the 
spinal  marrow,  viz.,  eight  from  the  region  of  the  neck,  twelve 
from  that  of  the  back,  and  five  from  the  pelvis.  By  examin- 
ing  the  above  cut,  it  will  be  seen  that  they  arise  by  two 
roots,  one  from  the  anterior,  and  one  from  the  posterior 
column.  The  fibres  of  the  posterior  swell  out  into  a  gang- 
Tion  before  they  unite  with  the  anterior. 

12* 


138  PHYSIOLOGY. 

7.  A  few-  years  ago,  Sir  Charles  Bell  discovered,  that  by 
opening  the  spinal  canal  in  a  living  animal,  and  dividing 
the  posterior  roots  of  the  nerves,  the  parts  to  which  they  are 
distributed  are  deprived  of  feeling.  The  limb  may  be  prick- 
ed or  lacerated  in  any  way,  without  the  animal  manifesting 
the  least  feeling,  or  indication  of  suffering,  while  at  the  same 
time  the  power  of  motion  remains.  He  also  found  that  when 
the  posterior  roots  were  divided,  sensation  was  destroyed, 
but  motion  remained.  One  of  Majendie's  experiments,  is 
interesting.  Availing  himself  of  the  fact,  that  the  introduc- 
tion o[  ?iux  vomica  into  the  system,  produces  violent  spasms, 
tremors,  and  rigidity  of  the  muscles  :  he  administered  it  to  an 
animal,  after  having  severed  the  anterior  roots  of  the  spinal 
nerves.  The  consequence  was,  that  while  all  the  muscles, 
whose  nerves  remained  entire,  were  thrown  into  a  state  of 
violent  spasm;  those  supplied  with  the  nerves,  whose  roots 
had  been  divided,  remained  unaffected. 

8.  The  spinal  cord  then  serves  to  connect  the  brain,  which 
is  the  common  centre  of  sensation  and  voluntary  motion, 
with  all  the  sensible  parts  of  the  body,  and  with  the  muscles, 
the  instruments  of  motion.  We  may  view  it  in  this  sense, 
as  forming  a  channel  of  communication  for  a  bundle  of 
nerves  running  from  the  brain  to  every  part  of  the  system 
to  carry  messages  from  the  will,  and  to  transmit  intelligence 
back  again,  as  if  all  the  roads  and  high-ways  in  the  country 
should  terminate  in  one  grand  post-road,  connecting  them 
with  the  seat  of  government. 

9.  To  illustrate,  suppose  I  seize  a  hot  iron  in  my  hand, 
not  knowing  it  to  be  heated  ;  the  painful  impression  is  im- 
mediately transmitted  along  the  sensiferous  nerves  to  the 
spinal  cord,  and  through  that  to  the  brain.  The  brain  takes 
cognizance  of  it,  and  a  mental  determination  is  immediately 
formed  to  drop  the  iron.  The  will  sends  back  its  command 
through  the  anterior  column  of  the  spinal  cord  to  the  motific 
nerves,  distributed  to  the  muscles,  which  go  to  the  hand. 
The  muscles  instantly  obey  ;   the  iron  drops,  and  the  whole 


THE  SPINAL  MARROW  AND  ITS  FUNCTIONS.  139 

process  occupies  but  an  instant.  Thus  we  have  two  channels 
of  nervous  influence  ;  the  one  transmitting  intelHgence  to 
the  mind,  the  other  conveying  the  purposes  of  the  will  to  the 
muscles  necessary  to  carry  them  into  effect. 

10.  That  such  is  the  chief  function  of  the  spinal  marrow, 
is  proved  by  the  well-known  fact,  that  if  it  is  divided 
in  any  part  of  its  course,  that  portion  of  the  body,  as  well 
as  the  limbs,  which  are  situated  below  the  seat  of  the 
injury,  will  be  paralyzed  ;  that  is,  all  sense  and  motion  will 
be  lost,  while  the  parts  above  the  injury  will  be  unaffected. 
If  the  injury  occur  very  high  up  in  the  neck  instant  death 
will  ensue,  because  the  nerves,  which  go  the  diaphragm  and 
are  necessary  to  carry  on  breathing,  are  separated  from  their 
connection  with  the  brain.  These  leave  the  spine  as  high 
as  the  third  "uerie&rcc  of  the  neck. 

11.  I  have  stated  that  it  has  been  proved,  that  the 
principle  of  motion  resides  to  some  extent  in  the  spinal 
marrow  itself.  This  is  shown  by  the  following  experiment. 
If  after  the  spinal  cord  be  divided  in  the  neck,  and  then  lower 
down  in  the  back,  we  irritate  any  of  the  muscles  which  are 
supplied  with  nerves  from  this  isolated  segment,  motion  will 
be  produced.  If  the  foot,  or  the  hand  be  pricked,  it  willim- 
mediately  contract ;  and  this  contraction  is  produced  by  the 
irritation  being  transmitted  to  that  portion  of  the  spinal  mar- 
row, from  whence  the  nerves  of  the  part  arise,  and  whose 
connection  with  the  brain  has  been  severed,  and  then  an  im- 
pulse is  sent  back  again  from  this  portion  to  the  muscles  of 
the  hand  or  foot  which  causes  them  to  contract.  Still,  all 
voluntary  motion,  as  well  as  sensation,  depend  on  the  brain. 

12.  If  the  meduUa  oblongata  is  injured,  breathing  imme- 
diately ceases.  If  the  spinal  marrow  is  severed  opposite  the 
second  bone  of  the  neck,  death  also  speedily  follows  ;  because 
the  nerves  of  respiration  are  cut  off  from  their  connection 
with  the  part  above.  If  the  spinal  cord  be  divided,  as  low  as 
the  ffth  cervical  bone,  then  life  will  not  be  immediately  de- 
stroyed ;  but  the  breathing  will  be  difficult ;  because  the  dia- 


140  PHYSIOLOGY. 

phragm  is  paralyzed,  and  death  sooner  or  later  follows  from 
suffocation.  If  it  be  divided  about  the  first  dorsal  vertehra^ 
then  life  may  be  maintained  for  a  considerable  time,  although 
the  ribs  cannot  be  elevated,  as  the  intercostal  muscles  are 
rendered  paralytic.  Breathing  is,  however,  kept  up  by  the 
action  of  the  diaphragm.  I  have  seen  a  man  whose  spine 
was  dislocated  in  this  region,  live  seven  or  eight  weeks.  All 
sensation  and  motion  were  lost  in  the  parts  below  the  seat  of 
the  injury,  but  his  reason  and  senses  were  perfect. 

13.  As  the  hearty  lungs,  larynx,  and  many  of  the  most  im- 
portant organs  of  the  body  are  supplied  with  nervous  influ- 
ence by  the  eighth  pair  of  nerves,  or  yar  vagum.,  why  is  it 
that  a  division  of  the  spinal  marrow  causes  death  ?  This 
question  is  easily  answered,  by  remembering  that  one  of  the 
functions  of  the  par  vagum  is,  to  convey  to  the  brain  the 
sense  of  the  want  of  air,  or  of  respiration,  and  that  this 
stimulus  reacts  xx^on  those  parts  of  the  spinal  cord  which  give 
rise  to  the  respiratory  nerves  of  the  chest.  Now  if  this  com- 
munication be  cut  off,  the  influence  of  the  brain,  or  the  me- 
dulla  oblongata,  cannot  be  transmitted  so  as  to  excite  those 
muscles  which  are  employed  in  breathing. 

14.  That  this  is  the  true  answer  to  the  above  question  is 
also  shown  by  dividing  the  par  vagum  in  the  neck.  This 
causes  palsy  of  the  lungs,  and  also  of  the  muscles  which  open 
the  larynx  ;  in  consequence  of  which,  the  top  of  the  wind- 
pipe is  immediately  closed,  and  death  follows  from  suffocation. 
Besides  this,  it  also  prevents  transmitting  to  the  meduUa  ob- 
longata, the  sense  of  the  want  of  respiration,  and  thus  pre- 
vents also  the  reaction  of  this  part  upon  the  spinal  marrow. 

15.  Does  the  spinal  marrow  exert  any  influence  upon  the 
circulation  of  the  blood  ?  It  is  ascertained  that  the  action  of 
the  heart  is  nearly  independent  of  the  spinal  marrow.  Its 
nervous  influence  is  derived  from  the  par  vagum  and  the 
great  sympathetic  nerve,  the  former  of  which  has  but  little 
connection  with  the  spinal  cord.  The  whole  spinal  marrow 
has  been  removed,  and  still  the  heart  has  continued  to  act. 


THE  SPINAL  MARROW  AND  ITS  FUNCTIONS.  141 

Its  action,  however  in  such  cases  is  much  weakened.  That 
the  heart  is,  however,  in  some  measure  influenced  by  the  spi- 
nal innervation,  must  be  admitted. 

16.  What  is  called  the  capillary  circulation,  or  that  in  the 
small  vessels,  is  much  under  the  influence  of  the  spinal  mar- 
row.  It  is  found  that  when  any  part  of  it  is  destroyed,  the 
blood  does  not  circulate  in  the  small  vessels  which  derive 
their  nerves  from  the  portion  destroyed.  In  these  cases,  the 
skin  becomes  'purple,  and  dry  ;  perspiration  ceases,  the  cuti- 
cle peels  off,  and  the  part  becomes  sensibly  colder.  The 
whole  nervous  system,  however,  is  concerned  in  the  produc- 
tion of  animal  heat. 

17.  Digestion  is  to  a  considerable  degree  under  the  influ- 
ence of  the  spinal  cord.  In  all  cases  of  diseases  of  the  spine, 
the  appetite  is  poor,  and  the  digestive  powers  weak.  Colic 
aiid  dyspepsia  are  frequent  attendants  upon  such  complaints. 
If  the  eighth  pair  of  nerves  be  divided,  the  stomach  is  imme- 
diately paralyzed,  and  digestion  interrupted.  This  shows 
that  the  stomach  depends  for  nervous  influence  on  the  me. 
dulla  oblongata,  and  that  it  is  derived  through  the  medium  of 
the  par  vagum. 

18.  The  spinal  marrow  exerts  an  important  influence  over 
the  kidneys,  more  so  perhaps  than  over  any  of  the  abdominal 
viscera.  Some  physiologists  also  think  that  it  presides  over 
the  functions  of  nutrition.  What  seems  to  confirm  this 
opinion,  is  the  fact,  that  in  the  Crustacea,  insects,  and  worms, 
which  have  the  power  of  speedily  reproducing  any  part  that 
is  cut  off,  the  spinal  marrow  preponderates  over  every  other 
portion  of  the  nervous  system.  Nutrition  is  known  to  depend 
chiefly  on  the  influence  of  the  great  sympathetic  nerve,  but 
its  connections  with  the  spinal  marrow  are  so  numerous  and 
intimate,  that  there  can  be  little  doubt,  it  derives  a  consider- 
able portion  of  its  nervous  energy  from  the  latter.  The  fol- 
lowing cut  represents  the  left  side  of  the  brain  and  spinal 
marrow,  shown  by  making  a  section  of  the  cranium  and  the 
spinal  column,  and  removing  the  dura  mater. 


142 


PHYSIOLOGY. 


THE  SPINAL  MARROW  AND  ITS  FUNCTIONS.         143 

a.  The  convolutions  of  the  cerebrum. 

h.  The  laminae  of  the  cerebellum. 

c.  The  pons  varolii. 

g.  The  medulla  oblongata. 

c.  d.f.  The  medulla  spinalis,  or  spinal  marrow,  extending  from  the 
first  cervical  to  the  first  lumbar  vertebra,  and  terminating  in  the  cauda 
equina.  The  cerebrum,  it  will  be  seen,  is  the  largest  portion  of  the 
brain,  and  occupies  the  whole  upper  cavity  of  the  skull.  It  rests  an- 
teriorily  upon  the  arches  of  the  orbits ;  in  the  centre,  upon  the  middle 
fossae  of  the  base  of  the  skull,  and  posteriorily  upon  the  tentorium 
cerebelli. 


Questions.— How  do  we  find  the  brain  developed  in  the  lower  ani- 
mals ?  Have  they  great  tenacity  of  life  ?  "Will  zoophytes  live  when 
divided  into  pieces  ?  What  is  the  medulla  oblongata  ?  What  its  func 
tion?  Describe  the  spinal  cord  ?— its  membranes?  its  shape?— its 
structure  ?  How  many  pair  of  nerves  arise  from  it  ?  How  many  from 
the  neck  ?— the  back?— the  loins?  What  is  the  function  of  the  ante- 
rior roots  ?— the  posterior  roots?  What  is  the  use  of  the  spinal  cord  ? 
How  is  this  illustrated?  How  proved?  What  follows,  if  the  spinal 
cord  be  severed  opposite  the  second  bone  of  the  neck  ?— the  fifth  ?— the 
first  dorsal  ?  Does  the  principle  of  motion  reside  to  any  extent  in  the 
spinal  cord  itself?  What  experiment  proves  this  ?  Why  does  a  divi- 
sion  of  the  par  vagum  or  eighth  pair  cause  death  ?  Does  the  spinal  mar- 
row exert  any  infiuence  on  the  circulation  of  the  blood  ?— on  the  capil- 
lary circulation  ?— on  digestion  ?  What  proves  this  ?  Has  it  any  in- 
fluence over  the  kidneys  ? — over  nutrition  ? 


CHAPTER  XII. 

THE  NERVES  AND  THEIR  FUNCTIONS. 

1.  In  describing  the  nerves  and  their  functions,  it  will  be 
necessary  to  classify  them,  or  to  reduce  them  to  such  arrange- 
ment, as  the  present  state  of  our  knowledge  on  the  subject 
will  admit.  The  following  comes  as  near  such  a  classifica- 
tion as  it  is  possible  to  make  : — 1.  Nerves  of  Special  Sense, 
2.  Motific  Nerves.  3.  The  Respiratory  Nerves.  4.  The 
Regular  Nerves^     5.  The  Ganglionic  Nerves. 

2.  First  Order. — The  nerves  which  contribute  to  the 
senses  of  sight,  hearing,  and  smell,  constitute  the  first  class, 
and  are  called  Nerves  of  Specific  Sense ;  because  they  are  in- 
capable of  communicating  any  other  impressions,  than  such 
as  belong  to  the  respective  senses  with  which  they  are  con- 
nected. For  example,  the  olfactory  can  only  transmit  ideas 
of  odours,  the  optic  of  colours,  the  auditory  of  vibrations, 
no  matter  what  the  stimulants  may  be  which  excite  thera 
to  action.  If  we  send  an  electric  shock  to  the  eye,  it  re- 
ceives the  impression  of  light ;  to  the  ear,  of  sound  ;  and  to 
the  nose,  an  odour  is  perceived  :  so  also,  if  we  press  or  strike 
the  ball  of  the  eye,  we  experience  a  vivid  sensation  of  light, 
and  the  same  phenomenon  occurs  when  the  eye  is  pierced  by 
the  needle  of  the  surgeon  :  so  also,  if  we  take  two  pieces  of 
different  kinds  of  metal  in  the  mouth,  and  placing  one  over, 
and  the  other  under  the  tongue — allow  their  edges  to  come 
together,  we  perceive  at  once  a  peculiar  taste,  excited  by 
galvanism.  Thus  do  these  nerves  communicate  to  the  mind 
that  they  are  affected  in  the  only  manner  of  which  they  are 
capable. 


THE  NERVES  AND  THEIR  FUNCTIONS.      145 


This  cut  represents  a  portion  of  nerve,  showing  the  filaments  of 
which  it  is  composed,  and  one  of  them  drawn  out. 

3.  First,  or  olfactory. — These  nerves  take  their  name 
from  "  olfactus,^^  the  smell,  as  they  are  essential  to  this  sense. 
They  are  the  softest  nerves  in  the  body,  and  more  closely 
connected  with  the  hemispheres  of  the  brain  than  any  other. 
They  lie  immediately  under  the  anterior  lobes  of  the  brain ; 
and  as  they  pass  on,  they  swell  into  a  bulb,  from  which 
numerous  fibres  issue,  and  pass  into  the  nose  through  a  plate 
of  one  of  the  bones  of  the  skull.  This  plate  is  pierced  with 
so  many  holes  for  transmitting  these  twigs  of  the  nerve,  that 
it  has  the  appearance  of  a  seive ;  and  from  this  circumstance 
is  called  the  ethmoid  bone.  The  olfactory  nerve  is  spread 
out  upon  the  lining  membrane  of  the  nose,  and  is  merely 
defended  by  a  thin  layer  of  mucus.  It  was  necessary  that 
these  nerves  should  come  to  the  surface,  in  order  to  come  in 
contact  with  the  vapours  inhaled  by  the  nostrils.  In  some 
animals  these  nerves  are  very  large,  especially  in  ruminants, 
but  in  others  they  are  entirely  wanting,  as  in  whales.  In 
fishes,  you  may  see  the  bulb  of  the  olfactory  placed  immedi- 
ately under  the  cup-like  nostril.  From  the  bulb,  the  nerve 
runs  backward  along  a  canal  filled  with  transparent  fluid, 
enters  the  skull,  and  joins  the  brain. 

4.  The  second,  or  optic. — These  are  the  largest  of  the 
cerebral  nerves,  and  can  be  traced  as  far  back  as  the  medulla 
oblongata  at  the  base  of  the  brain.  They  pass  along  the  base 
of  the  brain,  and  just  before  they  enter  the  orbits  they  unite 
with  each  other,  or  seem  to  decussate,  or  cross  each  other. 
In  some  fishes,  these  nerves  evidently  cross  without  union ; 
but  in  man,  it  is  now  pretty  well  established,  that  a  semi- 
decussation takes  place  ;  that  is,  one  half  of  the  right  optic 
nerve  crosses  to  the  opposite  side,  and  joins  a  half  of  the 

13 


146  PHYSIOLOGY. 

left  nerve  to  proceed  to  the  left  eye  ;  so  that  each  eye  receives 
its  optic  nerve  from  both  sides  of  the  brain  ;  the  right  sup- 
plying the  right  side  of  both  eyes,  as  the  left  does  its  cor- 
responding side  of  both.  After  the  nerve  has  entered  the 
orbit,  it  proceeds  forwards  to  the  ball  of  the  eye,  and  pene- 
trating the  coats  of  that  organ,  expands  into  a  very  delicate 
web,  or  nervous  net- work,  called  the  retina,  which  serves  to 
receive  the  image  of  objects  falling  upon  it. 

5.  The  auditory  nerve. — The  last  nerve  of  specific  sense, 
runs  along  with  another,  the  two  together  being  known  as 
the  seventh,  of  which  the  auditory  forms  the  soft  portion,  or 
portio  mollis.  It  arises  from  the  medulla  oblongata,  and 
goes  on  in  contact  with  the  hard  portion,  or  portio  dura,  to 
the  internal  auditory  passage,  which  they  enter.  Here  the 
soft  portion  spreads  out  into  a  great  many  small  branches, 
which  are  distributed  over  the  surface  of  the  internal  por- 
tions of  the  ear,  and  their  extremities  float  in  the  water 
contained  in  the  labyrinth,  fi'om  which  they  receive  vibra- 
tions which  produce  the  impressions  of  sound. 

6-  Second  order. — The  motif erous  nerves,  which  consti- 
tute the  second  order,  consist  of  three  nerves  ;  the  third,  the 
sixth,  and  the  ninth,  with  perhaps  a  branch  of  the  Jifth, 
These  take  their  origin  at  the  anterior  columns,  in  the  same 
line  with  each  other  ;  but  fibrils  of  sensation  afterwards  join 
them,  so  that  they  are  analogous  to  the  double-rooted  nerves 
of  the  spinal  marrow. 

7»  The  thi7'd  pair  rise  from  the  crura  of  the  brain,  and 
pass  forward  to  a  hole  in  the  bottom  of  the  orbit,  through 
which  they  enter,  and  supply  four  of  the  six  muscles  which 
move  the  eye,  and  also  the  muscle  which  moves  the  upper 
eye-lid,  thus  placing  these  muscles  under  the  command  of 
the  will.  Besides  this,  a  small  twig  of  the  fifth  nerve  swells 
but  into  a  ganglion,  and  then  joins  a  twig  from  the  third, 
which  go  on  together,  and  penetrate  the  coats  of  the  eye,  to 
which  they  impart  sensibility,  and  are  connected  with  the 
functions  of  the  iris.     It  is  worthy  of  remark,  that  here  the 


THE  NERVES  AND  THEIR  FUNCTIONS.      147 

general  law  is  kept,  viz.,  that  a  ganglion  is  formed  in  the 
sensific  nerves,  before  they  become  associated  with  the  fila- 
ments of  motion, 

8.  The  sixth  pair  arise  near  the  last,  and  also  enter  the 
orbit ;  here  they  are  entirely  expended  upon  the  muscle 
which  turns  the  eye  towards  the  temple.  Where  this  nerve 
has  been  injured  or  lost  its  power,  the  eye  is  permanently 
turned  in  towards  the  nose  ;  and  such  a  person  is  said  to  be 
cross-eyed. 

■9.  The  ninth  pair  arise  from  the  pyramidal  bodies,  and 
passing  through  holes  in  the  occipital  bone,  proceed  forwards 
towards  the  angle  of  the  jaw,  by  the  side  of  the  hyoid  bone 
of  the  tongue,  and  are  distributed  upon  the  muscles  between 
-the  lower  jaw,  hyoid  bone,  and  tongue,  the  motions  of  which 
it  regulates. 

10.  Third  Order.— This  division  embraces  what  Sir 
Charles  Bell  calls  the  respiratory  nerves.  These  are  not  only 
connected  with  the  function  of  respiration,  but  contribute  also 
to  the  expression  of  the  passions  and  emotions  of  the  mind. 
They  consist  of  the  fourth  ;  the  portio  dura ;  of  the  seventh, 
or  facial ;  the  eighth,  or  par  vagum  ;  the  phrenic  ;  and  the 
externcd  respiratory.  As  the  medulla  oblongata,  consists  of 
three  columns;  the  nerves  of  motion  arise  from  the  anterior, 
those  of  sensation  from  the  posterior  ;  while  the  respiratory 
nerves,  already  mentioEed,  spring  from  the  middle  portion, 
and  all  nearly  on  the  same  horizontal  plane. 

11.  The  fourth  nerve  supplies  the  superior  oblique  muscle 
of  the  eye,  which  rising  from  the  bottom  of  the  orbit,  runs 
along  the  roof  of  that  cavity,  till  it  comes  close  to  its  brim, 
where  it  terminates  in  a  small  tendon,  which  passes  through 
a  loop  or  pulley,  then  turns  back,  and  is  inserted  into  the 
posterior  part  of  the  ball,  so  that  its  contraction  turns  the 
eye  in  towards  the  nose.  When  the  will  ceases  to  control 
the  movements  of  the  eye,  it  comes  under  the  action  of  the 
superior  oblique  muscle.  We  see  this,  in  acute  bodily 
pain,  and  at  the  point  of  death,  when  the  voluntary  muscles 


148  PHYSIOLOGY. 

have  lost  their  power.  This  turning  of  the  eye  inward 
is  supposed  to  indicate  great  agony  ;  but  it  rather  shows 
that  all  suffering  has  ceased,  and  that  the  powers  and  sen- 
sation and  motion  are  lost.  If  we  raise  the  eye-lid  of  a 
person  asleep,  we  shall  find  the  eye  turned  in  the  same  direc- 
tion ;  also  in  fainting,  and  in  cases  of  suspended  animation. 
The  fourth  nerve  is  partly  then  under  the  influence  of  the 
will,  and  partly  independent  of  it, 

12.  The  seventh  nerve  consists  of  two  portions,  one  of 
which,  the  auditory,  has  already  been  described.  The  other 
portion  is  c^XeA  facial,  because  it  is  distributed  over  the  facer 
Its  origin  has  already  been  stated,  though  it  receives  filaments 
from  each  column  of  the  medulla  oblongata  ;  so  that  its 
function  is  complicated.  It  seems,  in  fact,  to  combine  the 
character  of  a  regular  nerve  and  one  of  instinctive  motion  ; 
it  enters  the  internal  auditory  passage  in  connection  with 
the  nerve  of  hearing,  then  entering  a  canal  in  the  temporal 
bone,  it  comes  out  just  before  the  ear,  and  spreads  out  over 
the  face  in  three  principal  branches,  called  'pes  anserina,  or 
goose's  foot,  from  its  resemblance  to  that  object. 

13.  The  Jifth  nerve  is  distributed  to  the  same  parts  on 
which  the  facial  is  ramified  on  the  face  ;  the  one  serving  for 
sensation,  the  other  for  expression.  Thus  when  the  facial 
nerve  is  divided,  or  its  functions  destroyed  by  disease,  the 
side  affected  loses  all  power  of  expression,  though  sensation 
remains  unaffected  ;  on  the  contrary,  if  we  divide  the  fifth 
pair,  sensation  is  entirely  abolished,  while  expression  remains. 
The  facial  nerve  not  only  communicates  the  purposes  of  the 
will  to  the  muscles  of  the  face,  but  at  the  same  time,  it  calls 
them  into  action  under  the  influence  of  instinct  and  sympa- 
thy. On  this  subject  a  late  writer  remarks,  "  How  expres- 
sive is  the  face  of  man  ?  How  clearly  it  announces  the 
thoughts  and  sentiments  of  the  mind !  How  well  depicted 
are  the  passions  on  his  countenance  !  tumultuous  rage,  abject 
fear,  devoted  love,  envy,  hatred,  grief,  and  every  other  emo- 
tion,  in  all  their  shades  and  diversities,  are  imprinted  there 


THE  NERVES  AND  THEIR  FUNCTIONS.      14'9 

in  characters  so  clear  that  he  that  runs  may  read  !  How 
difficult,  nay,  how  impossible  is  it  to  hide  or  falsify  the  ex- 
pressions which  indicate  the  internal  feelings !  Thus  con- 
scious guilt  shrinks  from  detection,  innocence  declares  its 
confidence,  and  hope  anticipates  with  bright  expectation." 

14.  The  eighth  'pair  of  nerves  consist  of  three  distinct  ^r- 
lions ;  the  first  of  which,  from  its  being  distributed  to  the 
tongue  and  throat  is  called  glosso-pharyngeal ;  the  second^ 
from  its  irregular  course  is  called  vagans,  or  the  wandering 
nerve  -,  and  the  third,  from  its  origin  from  the  spinal  marrow, 
is  called  accessory.  These  different  nerves  join  just  as  they 
are  about  to  escape  from  the  skull,  which  they  do  in  com- 
pany with  the  internal  jugular  vein,  and  as  soon  as  they 
emerge  they  form  connections  with  the  great  sympathetic. 

15.  The  vagans,  on  leaving  the  skull,  sends  off*  branches 
to  the  pharynx  and  esophagus,  also  to  the  larynx  and  the 
muscles  which  close  the  air  passage,  and  the  mucous  mem- 
brane covering  it.  Its  trunk  runs  down  the  neck  included  in 
the  same  sheath  with  the  carotid  artery  and  jugular  vein, 
and  enters  the  chest  wnder  the  collar  bone.  Here  a  branch 
is  given  off*,  which  locks  round  the  subclavian  artery  on  one 
side,  and  arch  of  the  aorta  on  the  other,  and  goes  up  to  the 
larynx,  hence  it  is  called  recurreiit.  It  supplies  those  mus- 
cles particularly  which  open  the  air  passage.  The  vagans 
sends  down  twigs  with  the  sympathetic  which  surround  the 
the  divisions  of  the  wind-pipe,  and  accompany  them  in  all 
their  ramifications  through  the  lungs.  It  also  sends  numer- 
ous twigs  to  the  heart,  stomach,  liver,  pancreas,  spleen,  in- 
testinal tube,  and  finally  with  the  sympathetic  nerve,  and  forms 
those  great  nervous  centres  or  ganglia  in  the  abdomen,  which 
supply  all  the  viscera  of  that  cavity  with  nervous  energy^ 

16.  ^\\Q  phrenic  nerve  derives  its  name  from  its  distribu- 
tion to  the  diaphragm,  which  at  one  time,  was  considered  as 
the  seat  of  the  soul.  It  passes  out  of  the  vertebral  canal  be- 
tween the  second,  third,  fourth,  and  sometimes  fifth  cervicai 

13* 


150  PHYSIOLOGY. 

vertebrae ;  it  runs  down  the  neck,  and  enters  the  chest  on 
the  outer  side  of  the  internal  jugular  vein. 

17.  The  external  respiratory  nerve  is  distributed  to  the 
intercostal  muscles,  and  those  which  extend  from  the  ribs  to 
the  shoulder,  and  which  are  occasionally  employed  in  labo- 
rious breathing.  It  is  through  the  instrumentality  of  the 
accessory,  phrenic,  and  external  respiratory,  that  the  mus- 
eles  employed  in  respiration  are  brought  into  action,  com- 
bined and  directed  with  the  proper  degree  of  force,  velocity, 
and  extent,  without  the  necessity  of  interference  of  the 
mind.  Though  to  a  certain  extent,  they  may  be  under  the 
influence  of  the  will,  yet  it  is  only  in  a  secondary  degree. 
No  one,  for  example,  can  long  suspend  the  movements  of 
respiration,  for  in  a  short  time,  instinctive  feeling  issues  its 
irresistible  mandates,  which  neither  requires  the  aid  of  erring 
reason,  nor  brooks  the  capricious  interference  of  the  will. 

18.  The  influence  of  this  order  of  nerves  in  the  expression 
of  the  passions,  is  strikingly  depicted  in  Sir  Charles  Bell's 
Treatise  on  the  Nervous  System.  "  In  terror,"  he  remarks, 
"we  can  readily  conceive  why  a  man- stands  with  his  eyes 
intently  fixed  on  the  object  of  his  fears,  the  eye-brows  eleva- 
ted, and  the  eye-balls  largely  uncovered  ;  or,  why  with  hesi- 
tating and  bewildered  steps,  his  eyes  are  rapidly  and  wildly 
in  search  of  something.  In  this  way  we  only  perceive  the 
intense  application  of  his  mind  to  the  objects  of  his  appre- 
hension, and  its  direct  influence  on  the  outward  organs. 
But  when  we  observe  him  farther,  there  is  a  spasm  in  his 
breast ;  he  cannot  breathe  freely  ;  the  chest  remains  elevated, 
and  his  respiration  is  short  and  rapid ;  there  is  a  gasping 
and  convulsive  motion  of  his  lips,  a  tremor  on  his  hollow 
cheeks,  a  gasping  and  catching  of  his  throat ;  his  heart 
knocks  at  his  ribs,  while  yet  there  is  no  force  in  the  circu- 
lation, the  lips  and  cheeks  being  ashy  pale." 

19.  "  To  those  I  address,  it  is  unnecessary  to  go  farther 
than  to  indicate  that  the  nerves  treated  of  in  these  papers 
are  the  instruments  of  expression,  from  the  smile  upon  the 


THE  NERVES  AND  THEIR  FUNCTIONS.      151 

infant's  cheek  to  the  last  agony  of  life.  It  is  when  the 
strong  man  is  subdued  by  this  mysterious  influence  of  soul 
on  body,  and  when  the  passions  may  be  truly  said  to  tear 
the  breast,  that  we  have  the  most  afflicting  picture  of  human 
frailty,  and  the  most  unequivocal  proof,  that  it  is  the  order 
of  functions  we  have  been  considering  that  is  thus  affected. 
In  the  first  struggles  of  the  infant  to  draw  breath,  in  the 
man  recovering  from  a  state  of  suffocation,  and  in  the  agony 
of  passion,  when  the  breast  labours  from  the  influence  at  the 
heart,  the  same  system  of  parts  is  affected,  the  same  nerves, 
the  same  muscles,  and  the  symptoms  or  characters  have  a 
strict  resemblance." 

20.  Fourth  Order. — Regular  Nerves. — I  have  already 
stated  that  there  are  thirty  pair  of  regular  nerves  which  go 
out  from  the  spine  ;  each  nerve  being  composed  of  two  kinds 
of  fibres  ;  those  of  the  anterior  column  being  subsidiary  to 
motion,  and  those  from  the  posterior  to  sensation.  With 
these,  physiologists  now  class  the  fftli  nerve.  This  large 
nerve  divides  into  three  principal  branches  ;  i\\Q  first  going  to 
the  eye,  is  called  opthalmic  ;  the  second  to  the  upper  jaw,  is 
called  superior  maxillary ;  and  the  third  sent  to  the  lower  jaw, 
is  named  inferior  maxillary.  It  is  the  third  branch,  how- 
ever, which  is  truly  a  compound  nerve,  as  its  roots  arise  both 
from  the  anterior  and  posterior  columns.  The  inferior 
maxillary  branch,  is  a  nerve  of  both  sense  and  motion ; 
its  filaments  of  motion  supply  the  muscles  which  shut  the 
jaw,  while  those  of  sensation  go  to  the  tongue,  salivary 
glands,  gums,  teeth  of  the  lower  jaw,  external  ear,  cheek, 
chin,  and  lower  lip.  It  is  this  nerve  which  gives  sensibility 
to  the  face,  and  it  is  this  which  is  the  seat  of  that  painful 
affection  called  tic  dolouroux,  which  is  sometimes  removed  by 
cutting  the  nerve  affected.  In  the  cat,  the  hare,  and  other 
animals  with  large  whiskers,  the  filaments  of  this  nerve  can 
be  traced  to  the  bulbs  of  the  hairs,  which  accounts  for  the 
delicate  tact  which  these  animals  are  endowed  with,  and  by 
means  of  which  they  are  enabled  to  wind  their  way  in  the 


152  PHYSIOLOGY. 

dark,  through  intricate  passages,  with  the  greatest  facility* 
The  fifth  nerve  is  associated  with  the  organs  of  the  senses 
of  smell,  sight,  and  hearing  ;  it  exercises  that  of  touch,  is 
the  immediate  instrument  of  taste,  and  is  affected  in  some 
degree  by  pungent  odorous  substances,  by  light,  and  by 
sound. 

21.  Spinal  nerves. — The  nerves  of  the  spinal  cord  are  all 
similar  in  their  construction,  and  in  the  functions  which 
they  perform.  The  two  sets  of  filaments  of  which  they  are 
composed,  though  enclosed  in  the  same  sheath,  yet  remain 
entirely  distinct  throughout  their  entire  course.  They  go 
to  every  muscular  fibre  in  the  system,  and  spread  out  over 
the  entire  surface  of  the  body,  which  possesses,  accordingly, 
a  more  exquisite  sensibility  than  the  deep-seated  parts. 
Thus  in  amputating  a  limb,  the  chief  pain  is  in  cutting 
through  the  external  parts  ;  for  the  bone  may  be  sawn 
through,  the  muscles,  tendons,  and  ligaments  cut  and  la- 
cerated, and  even  burnt  v/ith  a  red-hot  iron,  and  still  the 
patient  experiences  little  or  no  suffering. 

22.  The  object  of  endowing  the  skin  with  such  a  high 
degree  of  sensibility,  is,  doubtless,  to  warn  us  to  avoid,  not 
only  what  is  injurious  to  the  skin  itself,  but  also  what  might 
endanger  internal  parts.  It  thus  serves  as  a  protector  to 
the  whole  body.  The  extremes  of  heat  and  cold,  which 
might  prove  injurious,  produce  their  painful  impressions  ; 
mechanical  ca^ises  rouse  by  their  sharpness,  roughness,  or 
hardness  ;  acrid  and  corrosive  chemical  agents  induce  un- 
easy sensation — all  which  serve  to  admonish  us  to  shun  the 
causes  producing  such  effects.  It  is  remarkable  to  notice 
how  every  part  of  the  body  is  endowed  with  its  own  kind 
of  sensibility.  The  skin  feels  changes  of  temperature ;  the 
muscles  experience  only  a  sense  of  fatigue  ;  the  eye  is  sen- 
sible only  to  light ;  the  ear  to  sound  ;  the  nose  to  odours  ; 
the  heart  to  blood  ;  the  stomach  to  food,  &c.  ;  and  these 
sensations  are  sent  along  up  to  the  brain  by  little  threads, 
in  close  contact  with  other  threads,  which  bring  back  the 


THE  NERVES  AND  THEIR  FUNCTIONS.      153 

commands  of  the  will !    Truly  may  it  be  said,  "  man  is  fear- 
fully and  wonderfully  made." 

23.  The  spinal  nerves  are  classed  according  to  the  por- 
tion of  the  spinal  column  from  which  they  issue  ;  as  the 
neck,  back,  loins,  and  pelvis  ;  forming  eight  cervical,  twelve 
dorsal,  five  lumbar,  and  five  sacral  nerves  ;  all  being  con- 
nected with  the  sympathetic.  The  four  lower  cervical  and 
first  dorsal  go  to  the  arm-pit,  where  they  form  a  complicated 
plexus,  from  whence  nerves  issue  to  supply  the  arm  and  hand. 
The  dorsal  nerves  supply  the  integuments  of  the  body,  the 
intercostal  muscles,  and  those  of  the  chest.  The  lumbar 
and  sacral  nerves  supply  the  muscles  of  the  loins  and  abdo- 
men, together  with  the  lower  limbs. 

24.  Fifth  Order. — Ganglionic  Nerves. — We  have  now 
considered,  somewhat  minutely,  that  portion  of  the  nervous 
system  which  is  called  the  cerebro-spinal,  embracing  the 
brain,  the  material  instrument  of  thought,  the  source  and 
channels  of  voluntary  motion,  and  of  instinctive  movements 
and  sympathy.  The  ganglionic  nerves  are  sometimes  called 
great  sympathetic^  or  the  great  intercostal;  but  sympathy 
has  been  shown  to  be  chiefly  independent  of  it,  except  so 
far  as  it  receives  filaments  from  the  cerebro-spinal  nerves ; 
and  it  is  called  great,  not  so  much  from  its  size,  as  from  its 
supposed  importance. 


A  plexus  of  nerves. 


154  PHYSIOLOGY. 

25.  The  ganglionic,  or  great  sympathetic  nerve,  consists  in 
a  series  or  chain  of  gangUons,  extending  from  the  base  of 
the  cranium  to  the  extremity  of  the  sacrum.  They  are 
placed  on  the  lateral  part  of  the  bodies  of  the  vertebrae,  and 
are  united  to  each  other  by  intermediate  nervous  cords,  and 
send  off  continually  filaments  to  all  the  adjacent  organs. 
With  the  exception  of  the  neck,  there  is  a  ganglion  for  each 
intervertebral  space,  both  of  the  true  vertebrae  and  sacrum. 
Besides  these,  there  are  other  ganglia  situated  around  the 
trunks  of  some  of  the  large  vessels  of  the  abdomen.  These 
ganglia  are  composed  of  a  mixture  of  cineritious  and  medul- 
lary matter,  and  are  supposed  to  be  the  centres  of  peculiar 
nervous  power. 

26.  As  to  the  functions  of  this  order  of  nerves,  there  is 
good  reason  to  believe  that  the  peculiar  vitality  of  every 
organ  in  the  body  directly  depends  on  them.  Most  physi- 
ologists believe  that  they  preside  over  the  involuntary  func- 
tions,  as  secretion,  nutrition,  absorption,  calorification,  &;c. 
Others  suppose  that  the  office  of  the  ganglions  is  to  render 
the  organs,  which  are  supplied  with  nerves  from  them,  inde- 
pendent of  the  will.  As  branches  from  them,  accompany 
the  blood-vessels  throughout  their  course,  every  part  of  the 
body  must,  to  a  certain  extent,  be  under  their  influence. 

27.  There  have  been  thr^e  hypotheses  prevalent  in  respect 
to  the  functions  of  the  nerves.  The  jirsty  that  the  brain 
secretes  a  fine  fluid,  which  circulates  through  the  nerves, 
called  animal  spirits,  and  which  is  the  medium  of  communi- 
cation between  the  different  parts  of  the  nervous  system  ; 
the  second  regards  the  nerves  as  cords,  which  transmit  all 
impressions  by  a  kind  of  vibration ;  and  the  third  ascribes 
nervous  influence  to  electricity  or  galvanism.  But  there 
is  no  proof  whatever  of  the  existence  of  any  such  fluid  ; 
the  doctrine  of  vibrations  is  pretty  much  abandoned  ;  while 
the  electrical  hypothesis,  though  at  first  view  perhaps 
more  plausible,  has  probably  no  better  foundation  to  rest 
upon. 


THE  NERVES  AND  THEIR  FUNCTIONS.       155 

Questions. — How  are  the  nerves  classified  ?  What  nerves  consti 
tute  the  Jirst  order  ?  Why  called  nerves  of  specific  sense  ?  Describe 
the  first  or  olfactory.  Is  it  large  in  animals  ? — in  fishes? — in  whales? 
— Describe  the  second,  or  optic.  Do  the  fibres  cross  each  other  ? — its 
function  ?  Describe  the  auditory  nerve.  What  nerves  constitute  the 
second  order  ?  Where  do  they  arise  ?  Describe  the  third  pair  ; — their 
function  ?  Describe  the  sixth  pair  ; — their  function  ? — The  ninth  pair  ; 
— their  function  ?  What  compose  the  third  order  of  nerves  ?  Describe 
the  fourth  nerve  ; — its  function  ?  Describe  the  seventh  nerve  ; — its 
function  ?  The  fifth  nerve  ; — its  function  ; — distribution,  &c.  ?  Des- 
cribe the  eighth  pair  of  nerves.  What  are  its  three  branches  called  ? 
Describe  the  vagans  ; — the  recurrent ; — the  phrenic  ; — the  external 
respiratory  ?  What  does  Sir  Charles  Bell  say  of  the  influence  of  this 
order  of  nerves  ?  What  compose  the  fourth  order  of  nerves  ?  Why  is 
the  fifth  nerve  classed  with  the  regular  nerves  ?  Where  does  its  first 
branch  go  ; — its  second ; — its  third  ?  What  nerve  is  aifected  in  tic 
doloreaux  ; — its  function  ?  Describe  the  spinal  nerves  ; — their  mode 
of  origin  ; — their  distribution  ?  Why  is  the  skin  so  sensible  ?  Has 
any  part  of  th&  body  its  own  sensibility  ?  Illustrate  this.  How  are  the 
spinal  nerves  classed  ?  What  compose  the  fifth  order  7  What  other 
names  for  the  ganglionic  nerves  ?  Describe  them.  What  is  the  func- 
tion of  the  ganglionic  nerves  ?  What  hypotheses  have  prevailed  in 
relation  to  the  functions  of  the  nerves  ? 


CHAPTER  XIII. 

THE    FIVE    SENSES. SENSE    OF   TOUCH. 

1.  A  sensation  is  the  perception  of  an  impression  made  on 
some  organ.  By  our  sensations  we  receive  a  knowledge  of 
what  is  passing  within  or  without  the  body.  They  are  ac- 
cordingly divided  into  internal  and  external.  An  internal 
sensation^  is  one  which  is  produced  by  causes  acting  within 
the  system,  as  hunger  and  thirst ;  but  an  external  sensation 
is  one  that  is  occasioned  by  the  impression  of  a  body,  exter- 
nal to  the  part  impressed,  as  sight,  hearing,  &>c. 

2.  No  sensation,  we  have  seen,  can  be  perceived  unless  it 
is  transmitted  to  the  brain.  When  ideas,  which  have  been 
called  "  the  images  of  sensible  objects,"  are  reflected  upon 
and  compared  with  each  other,  we  exert  thought  and  judg- 
ment ;  and  when  they  are  recalled,  we  are  said  to  exert  the 
memory.  Thus  are  the  senses  avenues  to  knowledge,  though 
they  do  not  give  rise,  as  some  have  stated,  to  our  intellect 
and  moral  powers.  With  every  sense  an  animal  discovers 
a  new  world  ;  thus  creation  is  to  it  increased  or  diminished, 
accordingly  as  its  senses  are  more  or  less  numerous.  A 
sensation  lasts  a  certain  time  after  the  exciting  cause  has 
ceased.  Thus  if  a  piece  of  wood,  with  one  end  ignited  is 
whirled  round,  we  see  a  luminous  ring  ;  the  sensation  pro- 
duced by  the  wood  in  each  point  of  the  circle  continuing 
till  the  wood  arrives  at  that  point  again  ;  a  rocket  forms  a 
train. 

3.  The  external  senses  are  Jive  in  number ;  touch,  taste, 
smell,  hearing,  and  vision.  These  are  all  situated  at  the  sur- 
face of  the  body,  so  as  to  be  capable  of  acting  on  external 
bodies.  Most  of  them  are  under  the  control  of  the  will  ;  at 
least  they  may  be  exercised  actively  or  passively,  and  by 


SENSE    OF    TOUCH.  157 

directing  the  attention,  the  impression  may  be  rendered  more 
vivid. 

4.  The  sense  of  touch  is  the  general  feeling  or  sensibility 
produced  by  the  skin,  and  which  instructs  us  regarding  the 
general  qualities  of  bodies.  It  resides  also  to  some  extent 
in  mucous  membranes,  as  in  the  mouth,  throat,  &c.,  although 
in  a  very  imperfect  degi*ee.  For  example,  we  cannot  feel 
the  pulse  by  placing  the  tongue  over  it  on  the  wrist,  as  any 
one  can  ascertain  by  trying  the  experiment.  The  sense  of 
touch  is  distinguished  by  some  writers  from  that  oi  feelings 
but  they  are  only  modifications  of  the  same  sense. 

5.  I  have  already  given  some  account  of  the  structurc  of 
the  skin,  and  stated  that  it  is  divided  into  four  layers,  viz.^ 
the  cuticle^  mucous  web,  papillary  body,  and  true  skin ;  and 
that  the  cuticle  is  the  thin,  transparent  pellicle,  or  membrane, 
which  forms  the  external  incrustment  of  the  body,  protecting 
those  papillae,  in  which  reside  the  sense  of  touch.  As  no 
blood-vessels  or  nerves  have  been  traced  in  it,  it  is  supposed 
to  be  an  unorganized  texture,  or  an  albuminous  secretion, 
poured  out  by  the  subjacent  vessels,  and  hardened  by  the  in- 
fluence of  the  air.  This  accounts  for  its  rapid  formation, 
when  destroyed  by  a  blister,  burn,  <&c.  When  a  part  of  the 
body  is  exposed  to  irritation,  the  vessels  which  pour  out  the 
lymph,  from  which  the  cuticle  is  derived,  have  their  action 
increased,  and  the  cuticle  either  becomes  thickened,  as  in 
the  palms  of  the  hand  and  soles  of  the  feet,  or  the  effusion  is 
so  abundant  as  to  cause  a  separation  between  it  and  the  true 
skin,  causing  blisters. 

6.  Now,  it  is  a  general  law,  that  pressure  promotes  ab. 
sorption  ;  and  we  see  this  exemplified  daily  in  cases  of 
tumours,  abscesses,  bandaging  for  dropsical  effusions,  &;c. 
Had  this  tissue  been  subjected  to  this  general  law,  the  fric- 
tion and  pressure  to  which  the  cuticle  of  the  hands  is  ex- 
posed in  manual  labour,  and  of  the  feet  in  walking,  would, 
in  a  short  time,  have  entirely  deprived  them  of  protection, 
instead  of  rendering  their  covering  more  dense  and  thicker, 

14 


158  PHYSIOLOGY. 

that  it  may  more  effectually  serve  as  a  shield  to  the  parts  it 
covers.  As  the  cuticle  is  constantly  renewed  from  its  inter- 
nal surface,  it  is  also  constantly  peeling  off  in  the  form  of  a 
fine  powder,  or  thin  scales.  After  scarlet  fever,  and  other 
diseases,  attended  with  great  heat  of  the  skin,  it  is  entirely 
removed  ;  the  old  scarf-skin,  as  it  is  called,  being  thrown  off 
in  large  patches.  We  find  a  cuticle  in  all  organized  beings, 
plants,  as  well  as  animals,  though  it  differs  greatly  in  struc- 
ture and  appearance.  In  many  reptiles  and  crustaceous 
animals  it  is  entirely  shed  at  certain  periods,  presenting  an 
exact  mould  of  their  bodies,  their  scales,  and  other  external 
parts,  and  even  their  eyes  being  exactly  represented. 

7.  The  mucous  weh  has  already  been  pretty  fully  described. 
It  is  a  soft  p«lpy  net-work,  and  seems  to  consist  chiefly  of 
the  shaggy  extremities  of  blood-vessels,  interlaced  and  bound 
together  by  delicate  filaments  of  cellular  membrane.  It  is 
the  seat  of  those  minute  globules  which  constitute  the  colour- 
ing matter  which  vary  in  their  tints  in  different  races. 
These  tints  are  influenced  in  a  greater  or  less  degree  by 
climate,  for  we  find  in  tropical  countries  the  colours  of  both 
plants  and  animals  are  more  intense  and  brilliant  than  i» 
colder  regions,  and  that  exclusion  from  light  produces  a  pale 
blanched  appearance,  while  exposure  to  it  has  a  contrary 
tendency  ;  but  these  variations  are  neither  permanent  nor 
do  they  descend  to  the  offspring. 

8.  The  dermis,  or  true  skin,  is  the  thickest  part  of  the 
external  integuments,  and  is  composed  of  an  infinite  number 
of  plates,  consisting  of  filaments  inextricably  wound  together, 
and  abundantly  supplied  with  blood-vessels  and  nerves.  The 
external  surface  of  the  cutis  is  every  where  studded  by  very 
minute  nipples  or  papillae,  and  in  several  parts,  as  the  palms 
of  the  hands  and  the  ends  of  the  fingers,,  they  are  arranged 
in  symmetrical  rows,  which  form  wavering  lines,  and  separ- 
ated by  small  crevices  that  admit  of  the  flexions  of  the  skin 
and  its  adaptation  to  the  surfaces  of  external  objects.  These 
papillae  are  the  terminations  of  nerves  and  blood-vessels,  and 


SENSE    OF    TOUCH.  159 

are  the  immediate  instruments  of  touch.  Although  covered 
by  the  cuticle  and  mucous  web,  yet  the  removal  of  these  by 
blisters  or  otherwise,  does  not  increase  the  sense,  but  tends 
to  destroy  and  disturb  it.  From  this  arrangement,  sensation 
is  communicated  through  the  hair  and  nails,  as  well  as  the 
cuticle.  In  animals,  of  the  cat  tribe,  which  are  furnished 
with  whiskers,  these  serve  as  organs  of  touch,  as  their  roots 
terminate  in  these  nervous  papillae. 

9.  The  property  of  touch  belongs  to  every  part  of  the 
body,  though  the  hand  is  considered  as  its  special  organ. 
The  great  number  of  bones  of  which  it  is  composed,  make  it 
susceptible  of  every  variety  of  motion,  by  which  it  changes 
its  form,  and  adapts  itself  to  the  inequalities  of  the  surfaces 
of  bodies.  What  is  called  the  pulp  of  the  fingers,  seems 
composed  chiefly  of  a  tissue  of  blood-vessels  and  nerves, 
covered  by  the  cuticle  and  mucous  web,  and  supported  by 
the  nails.  The  delicacy  of  touch  is  vastly  improved  by 
education  and  practice.  This  is  shown  in  the  case  of  the 
blind,  who  often  can  distinguish  by  touch  the  different 
colours,  and  even  their  difTerent  shades.  This  will  not  ap- 
pear impossible  when  we  consider  that  difference  of  colour 
may  depend  on  the  dispositions,  arrangement,  and  number 
of  the  little  inequalities  which  roughen  the  surface  of  bodies, 
even  of  such  as  appear  the  most  polished,  and  thus  fit  them 
to  reflect  certain  rays  of  light,  while  they  absorb  the  others. 

•That  the  exercise  of  this  sense  is  a  gratification  to  the 
young,  is  apparent  from  the  eagerness  with  which  the  child 
stretches  out  his  little  hands  to  all  the  objects  within  his 
reach,  and  the  pleasure  he  seems  to  take  in  touching  them, 
in  all  their  parts,  and  running  over  all  their  surfaces, 

10.  I  have  already  mentioned  that  the  external  surface  of 
the  body  is  endowed  with  this  special  sensibility,  not  only 
that  it  might  furnish  us  with  a  knowledge  of  the  characters 
of  external  gbjects,  and  so  lead  us  to  avoid  dangers  which 
surround  us,  but  also  to  be  a  source  of  positive  pleasure. 
Though  in  the  acuteness  of  the  other  senses  many  animals 


1 60  PHYSIOLOGY, 

surpass  man,  yet  in  the  exquisite  sensibility  of  his  skin,  man 
stands  unrivalled.  "  The  skin  of  man,"  says  Majendie,  "  is 
more  delicate,  fuller  of  nerves  than  that  of  the  mammiferae  ; 
its  surface  is  covered  only  by  the  epidermis,  insensible  in- 
deed, but  so  thin,  that  it  does  not  intercept  sensation,  whilst 
the  hairs  which  cover  so  thickly  the  body  of  quadrupeds,  the 
feathers  which  clothe  that  of  birds,  quite  deaden  it.  The 
hand  of  man,  that  admirable  instrument  of  his  intelligence, 
©f  which  the  structure  has  appeared  to  some  philosophers,  to 
explain  sufficiently  his  superiority  over  all  living  species ; 
the  hand  of  man,  naked,  and  divided  into  many  moveable 
parts,  capable  of  changing  every  moment  its  form,  of  exactly 
embracing  the  surface  of  bodies,  is  much  fitter  for  as- 
certaining their  tangible  qualities,  than  the  foot  of  the  quad- 
ruped,  inclosed  in  a  horny  substance,  or  than  that  of  a  bird, 
covered  with  scales  too  thick  not  to  blunt  all  sensation." 

11.  The  hand  then,  is  the  chief  organ  of  touch,  and  in  the 
ends  of  the  fingers  it  resides  in  the  greatest  perfection.  Thus 
we  see  that  the  blind  are  able  to  read  with  facility  by  passing 
their  fingers  over  the  letters,  which  are  raised  by  a  particu- 
lar kind  of  type.  In  this  manner  they  acquire  a  knowledge 
of  geography,  arithmetic,  reading,  and  the  usual  branches  of 
education,  not  often  met  with  even  in  those  who  have  the 
use  of  their  eyes  as  well  as  their  hands. 

12.  Buffbn,  the  celebrated  naturalist,  thought  so  much  of 
the  sense  of  touch,  that  he  believed  the  cause,  why  one  per- 
son has  more  intellect  than  another  is,  his  having  made  bet- 
ter use  of  his  hands  from  early  infancy.  Other  philosophers, 
as  Majendie  states,  have  ascribed  man^s  superiority  over  ani- 
mals, and  his  intelligence,  to  the  fact  that  he  possesses  a 
hand.  But  the  hand  is  only  the  instrument  of  the  mind,  the 
agent  of  the  will ;  it  can  only  execute  ;  the  mind  must  plan. 
Besides,  the  idiot  has  sometimes  the  sense  of  touch  more  deli- 
cate than  the  man  of  genius,  or  than  the  most  skilful  artist ; 
while  some  of  the  most  ingenious  artists  have  by  no  means, 
the  most  delicate  touch.     Galen  truly  says,  that  man  had 


SEIfSE    OF    TOUCH.  161 

hands  given  him  because  he  was  the  wisest  creature  ;  but  he 
was  not  the  wisest  creature  because  he  had  hands.* 

13.  The  following  cases  prove  that  hands  are  not  indispen- 
sable to  genius,  and  that  the  human  mind  can  even  triumph 
over  the  imperfections  of  the  body.  A  few  years  since  a 
Miss  Biffin  was  exhibited  in  London,  who  was  entirely  destitute 
of  both  upper  and  lower  extremities ;  and  yet  she  was  very 
intelligent  and  ingenious.  She  could  hem-stitch  with  the 
greatest  facility,  turning  the  needle  very  rapidly  in  her 
mouth,  and  inserting  it  by  means  of  her  teeth.  She  also 
painted  miniatures  faithfully  and  beautifully,  holding  the 
pencil  between  her  head  and  neck.  All  her  motions  in  fact 
were  confined  to  the  tongue  and  the  lips,  and  to  the  muscles 
of  the  neck.  " 

14.  In  the  year  1825  there  was  a  young  artist  in  Paris, 
who  had  no  hands  or  arms,  and  only  four  toes  on  each  foot ; 
and  yet  he  sketched  and  painted  beautifully  with  his  feet.  I 
have  myself  seen  a  young  lady,  born  without  arms,  who  had 
acquired  so  much  skill  in  the  use  of  the  scissors  as  to  be  able, 
by  holding  them  in  her  mouth,  to  cut  likenesses,  watch-pa- 
pers, flowers,  &c.  She  would  also  draw  and  write,  and  exe- 
cute all  kinds  of  needle  work  with  her  mouth.  A  boy  was 
not  long  since  exhibited  in  the  museum  of  this  city,  who 
performed  all  these  things  with  his  toes.  This  shows  that 
other  parts  of  the  body  besides  the  fingers,  are  capable  of 
acquiring  great  delicacy  of  touch. 


*  On  this  subject  Dr.  Eiliotson  remarks,  "  As  philosophers  have 
ascribed  the  superiority  of  man's  intellect  to  his  hand,  and  of  the  ele- 
phant's to  its  trunk,  the  constructiveness  of  the  beaver  to  its  tail,  and 
the  ferocity  of  the  tiger  to  its  teeth  and  claws,  the  poor  man  may  be 
excused  who  was  lately  executed  at  Chelmsford,  and  left  the  following 
directions.  "  I,  Edward  Clarke,  now  in  a  few  hours  expecting  to  die, 
do  sincerely  wish,  as  my  last  request,  that  three  of  my  fingers  be  given 
to  my  three  children,  as  a  warning  to  them,  as  my  fingers  were  the 
cause  of  bringing  myself  to  the  gallows,  and  my  children  to  poverty/* 

14* 


162  PHYSIOLOGY. 

15.  In  animals,  the  organ  of  touch  varies.  In  the  ape 
tribe  it  is  similar  to  that  of  man.  In  some  quadrupeds  it 
is  seated  in  the  lipSf  snouts  or  probosciSf  as  in  the  horse,  the 
hog,  the  mole,  the  rhinoceros,  and  the  elephant.  Indeed, 
the  trunk  of  the  elephant  comes  very  near  to  the  human 
hand  in  nicety  of  touch,  and  delicaey  of  perception.  The 
hat  is  remarkable  for  sensibility  of  touch.  It  has  been  found 
that  if  its  eyes  were  destroyed  and  its  ears  and  nostrils  shut 
up,  it  would  fly  through  intricate  passages,  without  striking 
against  the  walls,  and  avoid  eveiy  object  placed  in  its  way. 
This  faculty  is  supposed  to  be  owing  to  the  great  delicacy  of 
touch  residing  in  the  membrane  of  the  wings,  which  feels 
instantaneously  any  change  produced  in  the  resistance  of  the 
air. 

16.  In  insects,  the  antenruB  or  feelers,  are  the  organs  of 
touch.  These  are  of  a  great  variety  of  forms,  very  flexible  4 
and  constantly  in  motion,  when  the  insect  is  walking.  If 
the  feelers  of  an  insect  are  cut  off*,  it  either  remains  motion- 
less, or  if  it  attempts  to  fly,  it  appears  bewildered  and  lost. 
It  is  by  means  of  their  feelers  that  bees  are  able  to  work  in 
a  hive  without  light,  and  build  their  cells  with  the  greatest 
regularity  ;  by  them  also,  they  communicate  to  one  another 
their  impressions  and  their  wants. 

17.  It  is  supposed  that  the  different  modes  in  which  ants 
touch  each  other  with  their  feders,  when  they  happen  to 
meet,  constitutes  a  kind  of  natural  language,  understood  by 
the  whole  tribe.  It  is  evident  that  they  could  not  co-operate 
in  their  labours  without  some  kind  of  language.  When  an 
alarm  is  given  in  time  of  danger,  one  ant  strikes  his  head 
against  the  corselet  of  every  ant  which  it  chances  to  meet, 
and  these  repeat  the  same  act  to  all  that  fall  in  their  way, 
and  so  the  news  is  quickly  spread  through  the  whole  society. 

18.  Sentinels  are  always  placed  on  the  outside  of  ants* 
nests  to  apprize  the  inhabitants  of  any  danger.  When  an 
enemy  approaches,  these  guardians  quickly  enter  the  nest 
and  spread  the  news  in  the  way  just  stated,  and  soon  the 


SENSE    OF    TOUCH.  163 

whole  swarm  is  in  motion.  While  a  larger  proportion  of 
the  ants  rush  out  to  repel  the  attack,  others,  who  have  the 
office  of  guarding  the  eggs  and  the  larvce,  or  eggs,  hasten  to 
remove  their  charge  to  places  of  greater. security.  These 
acts  all  depend  on  the  faculty  of  touch,  so  that  it  is  as  import- 
ant to  the  lower  animals  as  to  man. 

19.  Sight,  hearing,  and  touch,  have  been  called  intellec- 
tual senses,  because  they  are  the  means  through  which  we 
obtain  our  most  valuable  information,  the  witnesses  that  fur- 
nish the  evidence  of  the  existence  of  external  things.  We 
can  have  no  doubt  as  to  the  evidence  they  deliver,  if  they  all 
agree  in  their  report.  We  find  however  that  if  we  depend 
on  either  alone,  we  are  liable  to  be  deceived.  Sight  is  liable 
to  many  illusions  ;  we  may,  under  the  influence  of  the  ima- 
gination, or  of  a  diseased  brain,  imagine  that  we  see  a 
thousand  strange  sights,  ghosts,  hobgoblins,  spectres,  and 
devils  ;  or  from  similar  causes,  we  may  believe  that  we  hear 
strange  and  unearthly  sounds ;  but  if  we  attempt  to  touch 
the  objects  which  appear  to  present  themselves  to  our  vision, 
or  which  discourse  such  unnatural  music,  we  find  that  they 
vanish  before  us,  like  the  ignis  fatuus,  or  jack-o'lantern, 
which  we  may  chase  "  o'er  bog,  and  o'er  moor,"  but  we  can 
never  lay  our  hands  upon  it.  I  have  often  watched,  with  a 
degree  of  wonder,  the  action  of  a  patient  labouring  under 
drunken  delirium  ;  the  unhappy  maniac  not  only  sees  strange 
objects  about  hie  bed,  and  flitting  before  his  eyes,  but  he 
hears  them  singing  and  talking  to  him  ;  he  puts  out  his  hand 
to  grasp  them, — he  grasps  nothing, — still  he  is  not  unde- 
ceived, nothing  can  make  him  believe  that  what  he  sees 
and  hears  are  only  the  phantoms  of  a  diseased  brain  ;  he  per- 
sists in  endeavouring  to  seize,  to  touch  the  strange  objects, 
and  only  ceases,  when  after  days  and  nights  of  incessant 
vigilancp,  his  strength  exhausted,  he  either  sleeps  or  dies ! 

20.  Touch  has,  therefore,  been  relied  on  in  every  age,  as 
the  most  certain  of  our  senses,  and  it  is  well  to  recollect  that 
Ihe  most  important  fact  that  ever  occurred  on  the  theatre  of 


164  PHYSIOLOGY, 

this  earth,  viz.  the  resurrection  of  the  Saviour,  .is  established 
by  the  testimony  of  the  three  intellectual  senses.  In  the 
gospel  of  the  evangelist  St.  John,  we  read,  "But  Thomas, 
one  of  the  twelve,  called  Didymus,  was  not  with  them  when 
Jesus  came.  The  other  disciples  therefore  said  unto  him,  we 
have  seen  the  Lord.  But  he  said  unto  them,  except  I  shall 
see  in  his  hands  the  print  of  the  nails,  a-nd  put  my  finger  into 
the  print  of  the  nails,  and  thrust  my  hand  into  his  side,  I  will 
Bot  believe.  And  after  eight  days  again  his  disciples  were 
within,  and  Thomas  with  them  ;  then  came  Jesus,  the  door 
being  shut,  and  stood  in  the  midst,  and  said,  peace  be  unto 
you.  Then  saitK  he  to  Thomas,  reach  hither  thy  finger,  and 
behold  my  hands ;  and  reach  hither  thy  hand,  and  thrust  it 
into  my  side ;  and  be  not  faithless  but  believing.  And 
Thomas  answered  and  said  unto  him,  my  Lord  and  my  God. 
Jesus  saith  unto  him,  Thomas,  because  thou  hast  seen  me, 
thou  hast  believed ;  blessed  are  they  that  have  not  seen,  and 
yet  have  believed."  Thus  was  the  fact  of  the  resurrection 
established  by  the  evidence  of  so  many  of  the  senses,  as  ta 
render  deception  impossible. 

21.  In  some  instances  tiie  touch  itself,  is  liable  to  error.r 
For  example,  if  we  roll  a  pea,  or  a  bullet,  between  two  fingers 
crossed,  we  receive  the  impression  of  two  distinct  objects, 
though  we  know  there  is  only  one  ;  and  if  we  look  at  it,  at 
the  same  time,  the  illusion  is  not  removed,  though  we  see  at 
once  that  it  is  an  illusion.  The  organs  here  are,  however, 
placed  in  an  unnatural  position.  Another  fallacy  occurs 
with  respect  to  heat.  If  we  place  the  hand  in  separate  ves- 
sels, the  one  containing  warm,  and  the  other  very  cold  water, 
and  after  some  time  withdraw  the  hands,  and  immediately 
plunge  them  in  the  mixture  of  both  waters,  to  the  one  hand 
the  mixture  appears  warm,  and  to  the  other  cold.  So  in  a 
tropical  country,  if  one  person  descends  a  high  mountain 
from  the  regions  of  perpetual  snow,  and  meets  at  the  middle, 
another  ascending  from  the  hot  valley  below,  he  who  is  de- 
scending will  feel  oppressed  with  heat,  while  the  other  is 


SENSE    OF    TOUCH.  165 

shivering  with  cold,  and  both  sensations  are  produced  by  the 
same  temperature.  Frozen  mercury  excites  the  same  sensa- 
tion as  red  hot  iron.  A  piece  of  marble  will  feel  colder  than 
a  woollen  garment,  although  both  be  of  the  same  temperature, 
because  the  marble  is  a  better  conductor  of  heat  than  wool- 
len ;  a  deep  cellar  appears  warm  to  us  in  winter,  and  cold  in 
summer,  though  its  temperature  is  nearly  the  same  all  the 
year  round.  During  the  voyages  made  by  Captain  Parry 
to  discover  the  north-west  passage,  it  was  found  that  after 
having  lived  for  some  days  in  a  temperature  of  15  or  20  de- 
grees below  zero,  it  felt  quite  mild  and  comfortable  when  the 
thermometer  rose  to  zero  and  conversely.  The  sense,  there- 
fore, only  gives  us  an  idea  of  the  relative,  not  the  actual 
heat  of  bodies. 

22.  The  sense  of  feeling  may  become  blunted  to  an  extra- 
ordinary d^ree.  Chabert,  the  Fire  King,  was  said  to  have 
been  in  the  habit  of  swallowing  forty  grains  of  phosphorus 
at  once  ;  washing  his  hands  in  melted  lead  ;  and  drinking 
boiling  oil,  without  any  apparent  injury.  There  is  a  great 
'diifference  in  the  degree  of  sensibility  of  the  muooiiis  «iem- 
brane,  in  different  individuals,  some  being  able  without  in- 
convenience, to  swallow  fluids  of  a  temperature  which 
would  be  very  uncomfortable  to  others. 

23.  The  tactile  power  of  the  skin  is  not  proportionate  to 
its  sensibility.  Thus  the  arm-pits,  flanks,  soles  of  the  feet, 
and  other  parts  of  the  body,  have  slight  power  of  distinguish- 
ing objects  by  touch,  although  they  are  very  sensible.  It 
would  be  diflicult  to  make  a  person  laugh  by  tickling  the 
ends  of  his  fingers,  and  yet  we  have  seen  that  their  sense  of 
touch  is  more  delicate  than  that  of  any  other  portion  of  the 
skin.  All  the  surfaces  and  solids  of  the  body  possess  a  kind 
of  sensibility,  peculiar  to  themselves,  and  in  disease  may  give 
sensations,  but  this  a  diflferent  property  from  that  of  touch. 


Questions. — What  is  a  sensation  ?    How  are  they  divided?    What 


166  PHYSIOLOGY. 

is  an  internal  ?  What  an  external  sensation  ?  What  are  ideas  ? 
What  is  the  office  of  the  senses  ?  How  many  external  senses  are  there  ? 
Are  they  under  the  control  of  the  will  ?  What  is  touch  ?  Is  touch  the 
same  as  feeling  ?  Of  how  many  layers  is  the  skin  composed  ?  What 
is  the  cuticle  ?  How  formed  ?  Its  use  ?  Is  it  subjected  to  the  same 
law  as  the  other  parts  of  the  body  are  in  relation  to  pressure  1  What 
would  have  been  the  consequence  ?  Describe  the  mucous  web, — The 
true  skin.  Where  is  the  sense  of  touch  chiefly  situated  ?  Describe  the 
papillaj.  What  is  the  pulp  of  the  fingers  chiefly  composed  of?  Can 
the  blind  distinguish  colours  by  the  touch  ?  How  is  this  explained  ? 
Why  is  the  external  surface  endowed  with  special  sensibility  ?  What 
does  Majendie  say  of  the  human  skin?  By  what  process  are  the  blind 
enabled  to  read  ?  What  cases  show  that  the  possession  of  a  hand  is  not 
necessary  for  the  display  of  intellect  and  ingenuity  ?  What  is  the  or- 
gan of  touch  in  animals  ? — in  insects  ?  What  senses  are  liable  to  illu- 
sions ?  Which  is  the  most  certain  of  the  senses  ?  What  fact  was 
established  by  the  senses  of  hearing,  sight,  and  touch  ?  Is  the  touch 
ever  liable  to  error  ?  In  what  cases  ?  May  the  sense  of  feeling  be- 
come blunted  ?  What  facts  prove  it  ?  Are  the  tactile  powers  of  the 
ekin  in  proportion  to  its  sensibility  ? 


CHAPTER  XIV. 

SENSE    OF    TASTE. 


1.  The  sense  of  taste  is  allied  to  that  of  smell  and  touch, 
as  it  requires  the  immediate  contact  of  the  body  with  the 
organ  where  the  sense  resides.  The  quality  of  bodies, 
which  it  teaches  us,  is  called  sapidity.  The  superior  surface 
of  the  tongue  is  the  chief  organ  of  taste  ;  though  the  general 
lining  of  the  mouth  and  the  upper  part  of  the  throat  partici- 
pate  in  the  function.  The  tongue  is  chiefly  composed  of 
muscular  fibres,  running  almost  in  every  direction  ;  conse- 
quently  it  possesses  great  versatility  of  motion,  and  can  be 
moulded  into  a  great  variety  of  shapes.  It  may  be  con- 
sidered as  a  double  organ,  as  it  is  formed  of  two  symmetrical 
halves,  whose  boundaries  are  marked  by  a  slight  groove  in 
its  upper  surface  ;  dividing  it  into  right  and  left.  From 
this  groove  a  membranous  partition  extends  down  through 
its  centre,  and  is  attached  to  the  froenum  or  bridle  beneath. 
The  tongue  is  not  only  the  organ  of  taste  but  also  of  articu- 
lation,  and  also  aids  in  mastication  and  deglutition. 

2.  The  tongue  is  abundantly  supplied  with  blood-vessels  ; 
and  its  nerves,  as  we  have  seen,  are  supplied  from  three 
sources.  There  has  existed  great  difference  of  opinion 
among  physiologists,  as  to  which  of  these  three  is  the  special 
nerve  of  taste.  General  opinion  now  holds  the  fifth  as  the 
proper  nerve  of  taste,  as  well  as  of  sensibility  ;  the  ninth,  as 
that  of  voluntary  motion  ;  and  the  eighth,  as  the  means 
whereby  the  organ  is  brought  into  association  with  the 
throat,  gullet,  larynx,  &c.  Dr.  Elliotson,  however,  and  some 
others,  think   that   the   glosso-pharyngeal   is   the   nerve  of 

taste. 

3.  When  we  examine  the  surflice  of  the  tongue,  we  find 
it  thickly  studded  with  fine  papillae,  or  villi,  giving  the  organ 


168  PHYsioLOGrr. 

a  velvety  appearance.  There  are  three  varieties  of  these 
papillae.  The  first  are  situated  near  the  root  of  the  tongue, 
and  belong  to  the  class  of  mucous  follicles,  whose  office  it  is 
to  furnish  this  secretion.  These  are  much  larger  than  the 
others,  and  are  called  lenticular^  from  being  shaped  like  a 
lens.  It  is  these,  together  with  the  almonds  of  the  throat,^ 
or  ears,  as  they  are  sometimes  called,  which  afford  the 
mucus  to  lubricate  the  food  in  the  act  of  deglutition,  and 
also  to  keep  the  tongue  moist^and  in  a  condition  for  the  due 
performance  of  its  function* 

4.  The  other  two  sets  of  papillae  are  the  instruments  of 
taste.  The  one  set  is  named  conical,  or  filiform,  and  con- 
sists of  small  nipple-shaped  bodies,  broader  at  the  base  than 
the  top,  and  scattered  over  the  whole  surface  of  the  tongue, 
giving  it  its  rough  or  shaggy  appearance.  The  other  set 
of  papillae  is  larger,  and  consisting  of  small  rcKjnded  heads, 
supported  on  short  stalks,  something  in  the  shape  of  a  mush- 
room, they  have  been  called  fungiform.  These  are  but  iew 
compared  with  the  former.  These  sensitive  papillae  are 
supplied  with  numerous  blood-vessels  as  is  shown  in  the  next 
cut.  In  order  for  the  exercise  of  taste,  it  is  necessary  for  the 
mucous  membrane  to  be  in  a  state  of  integrity,  for  if  it  be 
removed,  we  only  experience  a  sensation  of  pain.  The 
animal  papillae,  which  abound  on  the  sides  and  tip  of  the 
tongue,  appear  to  be  the  most  exquisitely  sensible.^  Certain 
bodies  seem  to  affect  one  part  of  the  more  than  another. 
Acids,  for  example,  act  especially  on  the  lips  and  teeth  ;  acrid 
bodies,  like  mustard  and  cayenne  pepper,  on  the  pharynx. 
We  read  of  cases  in  medical  works,  where,  after  the  tongue 
has  been  removed  by  disease,  or  a  surgical  operation,  persons 
could  still  speak,  spit,  chew,  swallow,  and  taste.  In  one 
case,  the  individual  could  distinguish  the  bitterness  of  sal 
ammonial,  and  the  sweetness  of  sugar  ;  and  Blumenbach 
mentions  a  young  man,  who  was  born  without  a  tongue,  and 
yet  when  blindfold,  could  distinguish  between  solutions  of 
salt  and  aloes  put  upon  his  palate* 


SENSE    OF    TASTE. 


169 


An  upright  section  of  one  of  the  papillae  of  the  tongue  very  greatly 
magnified,  and  split  open,  to  show  the  nerves  (engraved  white)  and  the 
blood-vessels  (black.) 

5.  The  process  of  taste,  then,  is  as  follows  : — ^When  a 
fluid  is  taken  into  the  mouth,  these  papillae  dilate  and  erect 
themselves,  being  endowed  with  the  property  of  adapting 
themselves  to  the  active  or  passive  condition  of  the  sense  of 
taste.  If  a  solid  portion  of  food  is  received,  it  is  first  touch- 
ed by  the  tip  of  the  tongue  and  brought  into  close  contact 
with  the  papillae  ;  when  if  it  be  dry  or  solid,  it  is  carried  to 
the  back  of  the  tongue  and  moistened  with  saliva,  which 
thus  becoming  impregnated  with  its  flavour,  and  flowing 
over  the  sides  of  the  tongue,  gives  to  the  papillae  a  percep- 
tion of  the  savoury  juices.  The  saliva,  or  spittle,  it  should 
be  recollected,  is  secreted  by  the  parotid  and  other  salivarir 

15 


170  PHYSIOLOGY, 

glands,  chiefly  during  the  process  of  mastication,  for  the 
purpose  of  moistening  the  food,  while  the  mucous  secretion 
is  to  keep  the  tongue  in  a  condition  to  receive  the  impression 
of  sapid  bodies.  For  example,  in  sickness,  and  especially  in 
fevers,  when  the  mouth  is  dry  and  parched,  owing  to  a  sup- 
pression of  this  secretion,  the  taste  is  entirely  lost,  showing 
that  the  membrane  of  the  tongue  must  be  kept  moist  in  order 
to  the  preservation  of  the  taste. 

6.  Insoluble  substances  are  totally  insipid,  because  in  order 
to  affect  the  nerves,  the  substance  must  be  in  such  a  state  as' 
to  penetrate  the  spongy  papillae.  It  is  supposed  that  the 
salts  which  enter  into  the  composition  of  the  saliva,  are  very 
efficient  agents  in  reducing  substances  to  a  proper  condition 
for  making  an  impression  on  the  gustatory  organ.  In  this 
way,  we  can  account  for  the  fact,  that  metals^  though  in- 
soluble in  water,  often  impart  a  peculiar  taste.  The  organs 
of  taste  are  also  powerfully  affected  by  metals,  so  applied  tG 
the  mouth  as  to  call  forth  electric  action.  If  we  place  one, 
kind  of  metal  on  the  tongue  and  another  under  it,  and  then 
bring  their  edges  together,  a  strong  sensation  is  experienced 
If  we  touch  the  surface  of  the  tongue  with  the  point  of  a 
wire,  connected  with  the  positive  pole  of  a  galvanic  battery, 
a  sour  taste  is  experienced  ;  while  the  negative  pole  excites, 
an  alkaline  taste.  These  phenomena  may  be  owing  either 
to  the  electric  action,  disengaging  from  the  saliva  an  acid 
in  one  instance,  or  an  alkali  in  the  other,  or  the  electric  ex- 
citement may  call  forth  the  special  sensibility  of  the  gusta- 
tory organ,  in  the  same  manner  as  it  causes  the  special 
sensibility  of  the  other  organs. 

7.  Savours,  like  odours,  are  innumerable,  and  as  they  dif. 
fer  so  much  from  each  other,  it  is  impossible  to  classify  them 
in  any  satisfactory  manner.  We  can  readily  understand 
what  is  meant  by  the  terms  sweet,  bitter ^  sour,  saline,  acrid,, 
&,c.,  yet  each  of  them  differs  in  intensity,  as  well  as  other 
shades  of  character.  For  example,  rectified  sugar,  brown 
sugar,  maple  sugar,  beet  sugar,  molasses,  honey,  &;c.,  are  all 


SEN'SE    OF    TASTE.  171 

sweet,  but  the  taste  of  each  is  different.  Linneus  and  Booer- 
haave  both  made  a  dassification  of  savours,  but  they  have 
never  beeu  generally  adopted  by  physiologists,  Adelon 
divides  them  into  two  kinds,  the  agreeable  and  disagreeable. 
But  even  this  division  is  not  founded  in  nature  ;  for  we  find 
the  old  adage  true,  that  "  one  man's  meat  is  another  man's 
poison."  Every  person  has  some  peculiarities  of  taste,  dis- 
likes to  particular  articles  of  food,  or  shades  of  difference  in 
the  appreciation  of  tastes,  which  may  be  constitutional,  or 
caused  by  association.  Besides,  the  taste  sometimes  be- 
comes unaccountably  morbid  or  depraved.  We  often  see 
children  devouring  chalk,  brick-dust,  ashes,  dirt,  and  slate- 
pencils,  when  if,  at  other  times,  they  were  required  to  swal- 
low such  articles,  as  medicine^  they  would  doubtless  deem  it 
a  peculiar  hardship, 

-8.  Savours  differ  as  to  the  permanence  or  transientness 
of  impression  which  they  leave  upon  the  organs  of  taste. 
Aromatic  and  bitter  substances  particularly  leave  their  taste 
in  the  mouth  for  a  long  time  after  they  have  been  swallow- 
ed ;  the  physician,  therefore,  when  he  wishes  to  administer 
some  nauseous  drug,  forestalls  the  sense  of  taste,  by  direct- 
ing one  of  these  substances  to  be  held  previously  in  the 
mouth.  There  is  a  common  experiment  on  this  subject, 
which  has  led  to  many  bets,  viz.,  giving  to  a  person  blind- 
fold, brandy,  rum,  gin,  or  any  other  spirituous  liquor  in  rapid 
succession,  and  see  whether  he  can  tell  one  from  another. 
In  a  short  time,  the  nerve  becomes  so  impregnated  with  the 
different  substances,  that  all  distinction  becomes  confounded. 
Tasters  of  wine,  tea,  &c.,  understand  this  principle  ;  for  we 
see  them  take  up  a  small  portion  and  move  it  over  the  whole 
surface  of  the  mouth,  so  as  to  extend  its  action,  and  then 
they  wait  for  some  time  after  the  impression  is  made  before 
ihey  taste  of  other  samples.  When  a  person  takes  a  medi- 
<;inal  draught,  he  gulps  it  down  as  quick  as  possible,  in  order 
that  it  may  come  in  contact  with  as  small  a  portion  as  pos- 
sible of  the  organ  of  taste. 


172  PHYSIOLOGY. 

9.  The  taste  is  greatly  under  the  influence  of  habit.  Many 
articles  which  at  first  excite  disgust,  being  taken  through 
fashion  or  necessity,  at  length  become  highly  grateful.  We 
need  only  name  tobacco,  and  perhaps  ardent  spirits.  The 
taste  for  these  substances  is  altogether  artificial,  no  one  be- 
ing fond  of  them,  when  taken  for  the  first  time.  Sach  per- 
version of  taste  often  becomes  national.  Thus  garlic  forms 
a  constant  ingredient  in  the  dishes  of  some  European  coun- 
tries.  The  most  celebrated  sauce  of  antiquity,  was  the 
Roman  garum,  prepared  from  the  half-putrid  intestines  of 
fish.  Another  of  their  favourite  condiments  was  assafoetida  ; 
and  this  is  still  in  high  repute  among  many  of  the  orientals. 
Rotten  eggs  are  highly  esteemed  by  the  Siamese,  and  fish  in 
an  advanced  state  of  decomposition  is  highly  relished  in  the 
northern  and  western  islands  of  Scotland.  Dried,  putrid 
mutton  is  habitually  eaten  in  Iceland,  and  epicures  in  every 
country  esteem  game  and  venison  a  greater  luxury,  if  in  a 
putrescent  state.  To  be  a  fashionable  epicure  of  the  present 
day,  requires  that  the  taste  should  be  educated  or  trained, 
like  a  sportsman's  setter.  It  is  then  prepared  to  scent  out,' 
with  infallible  certainty,  what  fashion  has  taught  it  to  relish 
as  choice  luxuries  ;  but  which  simple,  unadulterated  taste, 
rejects  as  fit  only  for  the  kennel  or  the  carrion  crow. 

10.  The  gratification  which  we  derive  from  eating  de- 
pends chiefly  on  the  state  of  the  stomach.  If  that  is  not  in 
a  condition  to  digest  food  properly,  no  matter  how  much  we 
may  generally  relish  any  particular  article  ;  it  will,  at  such 
times,  invariably  excite  disrelish  or  even  disgust.  So  also 
when  we  sit  down  with  a  keen  appetite  to  a  meal,  as  our 
hunger  is  appeased,  the  relish  proportionally  diminishes,  till 
at  length  we  reach  the  point  of  satiety,  and  if  we  persist, 
nausea  and  disgust  are  certain  to  succeed.  Here  then,  is 
another  wise  provision,  informing  us  with  infallible  cer- 
tainty when  we  have  taken  sufficient  food  to  supply  the 
wants  of  the  system.  The  ancient  Romans  availed  them- 
selves of  a  knowledge  of  this  law,  and  hence  were  in  the  habU 


SENSE    OF   TASTE.  173 

of  leaving  the  table  once  or  twice  during  a  meal,  and  after 
having,  by  means  of  an  emetic,  unloaded  the  stomach,  of  re- 
turning again  to  the  charge. 

11.  As  a  general  rule,  articles  that  are  agreeable  to  the 
taste,  are  safe  and  nutritious,  though  this  is  not  invariably 
the  case.  For  example,  prussic  acid  has  a  very  agreeable 
savour,  as  well  as  odour,  and  is  accordingly  used  to  impart  fla- 
vour to  dishes  and  liqueurs,  such  as  noyeau,  yet  prussic  acid 
is  one  of  the  most  powerful  poisons  in  nature.  Many  sub- 
stances which  at  first  are  highly  agreeable,  in  a  short  time 
lose  their  relish  ;  we  see  that  grocers  understand  this  prin- 
ciple, for  instead  of  forbidding  a  new  apprentice  from  eating 
sugar,  raisins,  honey,  and  molasses,  he  tells  him  to  eat  all  he 
wants,  knowing,  that  in  a  short  time,  his  appetite  will  be 
cloyed,  and  all  temptation  removed. 

12.  Among  animals,  we  find  a  great  difference  in  the  per- 
fection of  this  sense.  Some  enjoy  it,  doubtless,  in  as  great, 
if  not  a  greater  degree  than  man,  as  they  are  able  by  it  to 
distinguish  plants  that  are  nutritive  and  good  for  food,  from 
those  which  are  poisonous ;  and  accordingly  it  is  a  rare 
thing  for  animals  to  die  from  eating  such  vegetables.  Many 
insects  feed  on  the  leaves  of  poisonous  plants,  and  some  anir 
mals  eat  the  leaves  of  the  poison  ivy  without  injury.  There 
is  an  insect  which  feeds  on  the  leaves  of  the  tobacco,  and  the 
southern  planter  guards  against  its  ravages  by  a  process 
called  worming.  The  taste  also  in  animals  sometimes  be- 
comes morbid,  as  we  see  it  happen  among  our  own  race. 
Mr.  Bennet,  in  his  "Wanderings  in  New  South  Wales" 
states,  that  serious  losses  happened  to  the  farmers  in  that 
country  from  the  sheep  acquiring  the  habit  of  licking  and 
devouring  earth  impregnated  with  saline  matter.  In  a  short 
time,  he  says,  their  natural  innocent  dispositions  become 
changed,  and  they  become  carniverous  and  savage,  and  de- 
vour  the  lambs.  Thus  out  of  a  flock  of  twelve  hundred 
lambs,  eight  hundred  were  devoured  by  the  sheep  themselves. 

13.  The  sense  of  taste  is  most  delicate  in  youth.     It  is 

X5* 


174  ~  PHYSIOLOGY. 

much  impaired  by  the  use  of  alcoholic  drinks,  tobacco,  and 
highly  seasoned  food  ;  so  that  the  spirit-drinker,  the  tobacco- 
chewer,  and  the  epicure  often  lose  this  sense  to  such  a  de- 
gree that  they  cannot  rehsh  plain  dressed  food.  That  man 
relishes  his  food  best  who  rarely  uses  powerful  stimulants  and 
narcotics.  Majendie  says  that  man  would  probably  excel 
all  the  other  animals  in  delicacy  of  taste,  if  he  did  not,  at  an 
early  period,  impair  its  sensibility  by  strong  drinks,  or  by 
the  use  of  spices,  and  other  luxuries. 

14.  The  taste  may  be  improved  by  cultivation  like  any 
of  the  other  senses.  Dr.  Kitchener  states  that  some  epicures 
are  able  to  tell  from  what  precise  part  of  the  Thames  a  sal- 
mon had  been  caught,  when  presented  at  table.  Many 
gourmands  pretend  to  be  able  to  pronounce  by  sipping  a  few 
drops  of  wine,  the  country  whence  it  comes,  as  well  as  it& 
age  ;  to  tell  by  the  taste,  whether  birds  put  upon  the  table 
are  domesticated  or  wild,  &c.  Such  acuteness  of  taste  is 
however,  by  no  means  desirable,  as  we  are  liable,  in  the 
**  rough  and  tumble"  of  life,  to  meet  with  so  much  that  de- 
mands obtuseness  rather  than  refinement  of  feeling.  The 
epicure  with  his  acuteness  and  delicacy  of  taste,  is  liable  to 
continual  annoyances  and  discomforts,  while  the  man  of 
simple  and  unsophisticated  taste  will  receive  gratification 
and  pleasure  from  the  very  same  objects  which  excited  dis- 
gust in  the  former. 

15.  If  we  examine  the  lower  animals,  we  shall  find  that  in 
none  of  them  is  the  tongue  precisely  like  that  of  man.  The 
resemblance  is  the  nearest  in  apes ;.  but  in  them,  even,  it  is 
much  elongated.  In  animals  that  chew  the  cud,  or  ruminantSf 
we  find  the  tongue  covered  with  a  dense  cuticle,  studded 
over  with  numerous  pointed  papillae,  especially  towards  the 
root.  These  projections,  together  with  the  waving  ridges  on 
their  palates,  are  of  great  use  in  collecting  and  swallowing 
the  tender  herbage  on  which  they  feed.  In  the  cat  tribe, 
the  sharp,  horny  prickles  on  the  tongue,  enables  them  to  take 
a  firm  hold.     In  the  lion  and  tiger  these  prickles  are  suffi- 


SENSE    OF    TASTE.  "  175 

cient  to  tear  off  the  skin  even  of  large  animals.  Ant-eaters 
are  furnished  with  a  very  long  and  slender  tongue,  covered 
with  a  viscid,  adhesive  secretion,  whereby  they  are  able  to 
seize  their  prey,  on  thrusting  it  into  an  ant-hill. 

16.  Whales  have  an  enormous  tongue,  though  it  has  been 
doubted  whether  it  is  endowed  with  the  sense  of  taste.  They 
have,  moreover,  projecting  downwards  from  the  upper  jaw,  a 
kindof  pallisade,  consisting  of  several  hundred  plates  of  whale- 
bone, the  outer  edges  of  which  are  sharp,  the  inner  fringed 
with  long  hair  like  appendages,  the  spaces  between  the 
plates  being  little  more  than  half  an  inch.  The  length  of 
the  plates  sometimes  exceeds  twelve  feet.  This  pallisade, 
when  the  mouth  is  closed,  is  covered  by  the  enormous  fleshy 
lower  lip,  but  when  open,  it  presents  a  kind  of  grating 
through  which  the  water  loaded  with  medusce  and  other 
small  animals,  flows.  Captain  Parry  states  that  these  medu- 
scE  or  sea-hlubber,  so  abound  in  the  arctic  seas,  that  when 
the  water  is  still,  and  the  surface  smooth,  they  present  a 
striking  resemblance  to  a  thick  snow-fall,  when  the  flakes  are 
large  and  the  air  calm.  The  soft,  spongy  texture  which 
forms  the  tongue  of  the  whale,  is  thought  to  be  better 
adapted  for  licking  the  food  from  the  hairy  whale-bone  roof, 
and  transferring  it  to  the  gullet,  than  to  serve  as  an  instru- 
ment of  taste. 

17.  The  tongue  of  birds  varies  much  in  form  and  con- 
sistence. In  some,  it  is  horny,  as  in  the  toucan,  where  it  is 
several  inches  in  length  and  exceedingly  narrow,  like  a  long 
strip  of  whale-bone ;  or  in  the  wood-pecker,  to  the  tip  of 
whose  tongue  there  is  fixed  a  long,  sharp,  pointed,  spear-like 
body  with  serrated  edges,  for  piercing  and  seizing  on  insects 
burrowing  beneath  the  bark  of  trees.  Parrots,  which  belong 
to  the  same  class,  have  soft  fleshy  tongues  well  adapted  to  the 
exercise  of  taste. 

28.  In  reptiles  also,  we  find  great  variety  of  forms  and 
applications  of  the  tongue.  In  the  crocodile  it  is  small  and 
immoveable,  so  much  so,  as  to  lead  some  naturalists  to  deny 


176  PHYSIOLOGY. 

its  existence.  In  serpents,  it  is  forked,  and  susceptible  of 
considerable  motion ;  while  in  the  frog,  it  is  folded  back  in 
the  state  of  inactivity  ;  but  when  the  animal  is  about  to 
seize  an  insect,  it  suddenly  unfolds  and  projects  it  out  of  the 
mouth.  The  tongue  of  a  chameleon  is  contained  within  a 
sheath,  and  admits  of  being  projected  to  the  extent  of  six 
inches,  and  is  besmeared  with  a  glutinous  secretion.  In  the 
twinkling  of  an  eye  it  is  darted  out  to  catch  its  food,  which 
consists  chiefly  of  flies.  Fishes  have  the  mere  rudiments  of 
a  tongue,  fixed  near  the  throat,  which  is  often  furnished  with 
teeth.  There  is  reason  to  believe  that  many  of  the  inverte- 
brated  animals  are  endowed  with  taste,  such  as  bees,  wasps, 
flies,  and  leeches. 


Questions. — To  what  sense  is  that  of  taste  allied  ?  What  is  sapid- 
ity? What  is  the  chief  organ  of  taste  ?  What  other  parts  participate 
in  the  function  ?  Describe  the  structure  of  the  tongue.  From  what 
source  does  the  tongue  derive  its  nerves  ?  Which  is  the  nerve  of 
taste  ?  What  are  papillae  ?  How  many  kinds  are  there  on  the 
tongue  ?  What  is  the  office  of  the  mucous  papillae  ? — Of  the  conical 
and  fungiform  ?  What  is  the  process  of  taste  ?  Can  insoluble  sub- 
stances be  tasted  ?  Why  not  ?  What  are  the  use  of  the  salts  in  the 
saliva  ?  How  do  we  taste  metals  ?  How  is  the  taste  excited  by  gal- 
vanism explained  ?  Are  there  many  savours  ?  •  Name  some.  Can 
they  be  classified  ?  Why  not  ?  What  articles  leave  a  taste  in  the 
mouth  the  longest  ?  What  use  can  be  made  of  this  fact  ?  How  do 
tasters  manage  ?  Is  taste  under  the  influence  of  habit  ?  What  facts 
show  this  ?  To  what  is  the  pleasm-e  of  eating  owing  ?  How  is  this 
shown  ?  Is  the  taste  a  sure  guide  to  what  is  safe  and  nutritious  ?  Do 
animals  differ  as  to  taste  ?  Do  they  possess  it  in  as  great  perfection  as 
man  ?  Does  it  ever  become  morbid  in  them  ?  When  is  taste  most 
delicate  ?  How  is  it  impaired  ?  May  the  taste  be  improved  ?  Are 
the  advantages  or  disadvantages  the  greatest,  which  attend  great  deli- 
cacy of  taste  ?  Have  any  of  the  lower  animals  a  tongue  like  that  of 
man?  Describe  some  peculiarities?  What  apparatus  have  whales 
for  eating  small  sea  animals  ?  What  is  said  of  the  tongue  of  birds  ? — 
of  reptiles  ?  of  fishes  ?  Do  any  of  the  invertebrated  animals  possess  the 
faculty  of  taste  1 


CHAPTER  XV^^'  ii*- 


■s. 


THE    SENSE    OF    SI 


1.  The  sense  of  smell  takes  cognizance  of  the  odorous 
properties  of  bodies.  The  seat,  or  organ,  is  the  mucous 
membrane,  which  lines  the  nasal  cavities,  and  is  called  the 
schneiderian,  or  'pituitary  membrane.  It  is  covered  with 
nervous  papillae,  similar  to,  but  more  delicate  than  those 
which  cover  the  organ  of  taste.  These  cavities  open  an- 
teriorily  through  the  external  nostrils,  and  posteriorly  into 
the  fauces  or  throat,  to  permit  the  air  to  traverse  them  in 
its  passage  to  the  lungs.  The  nasal  organ  seems  to  be 
designed  for  the  purpose  of  collecting  the  odorous  particles ; 
and  it  is  divided  into  two  similar  cavities,  by  a  bony  parti- 
tion, called  the  «5omer,  which  is  extended  by  means  of  cartilage 
to  the  anterior  extremity  of  the  nose.     Each  nostril  contains 


Front  view  of  the  nasal  fossae. 


178 


PHYSIOLOGY. 


two  convoluted  or  turbinated  bones,  of  a  light  spongy  tex* 
ture,  one  being  situated  above  the  other  ;  and  they  divide 
the  general  cavity  of  the  nostril  into  three  passages. 

2.  In  connection  with  the  nostrils,  there  are  several  cavi- 
ties, as  in  the  frontal  and  upper  jaw-bones,  called  sinuses. 
These  communicate  with  the  nostrils,  and  as  they  extend 
the  surface  on  which  the  lining  membrane  is  expanded,  they 
are  supposed  to  contribute  to  the  sense  of  smell,  by  affording 
capacious  receptacles  for  air,  loaded  with  odorous  particles. 
Of  the  14  bones  which  enter  into  the  formation  of  the  face, 
11  assist  in  forminsr  the  cavities  of  the  nostrils,  as  do  also 
three  out  of  the  eight  bones  that  form  the  cranium.     Be- 


Nasal  fossae  seen  from  behind, 


SENSE    OF    SMELL.  179 

sides  the  cartilage  which  forms  the  septum  of  the  nose,  two 
others  of  an  elastic  nature  constitute  the  wings;  and  as  they 
admit  of  motion,  several  muscles  are  attached  to  them,  in 
order  to  regulate  the  external  orifices  in  accordance  with 
different  conditions  of  respiration,  and  also  to  enable  us  to 
exercise  the  sense  of  smell  with  greater  effect,  when  we  wish 
voluntarily  to  employ  that  function. 

3.  Tne  membrane  which  lines  the  nasal  fossae,  resembles 
the  mucous  membranes  generally,  and  adheres  firmly  to  the 
bones  and  cartilages  which  it  covers.  Externally,  this  mem- 
brane is  continuous  with  the  common  integuments,  and  pes. 
terioriy  with  the  lining  membrane  of  the  throat.  It  varies 
somewhat  in  appearance  in  different  situations.  In  the 
sinuses,  it  is  thin,  pale,  and  of  a  smooth  surface  ;  but  where 
it  constitutes  the  immediate  seat  of  smell,  it  is  thicker,  more 
vascular,  and  of  a  redder  colour  than  mucous  membrane  in 
other  situations.  It  is  studded  with  mucous  follicles,  which 
yield  the  secretion  with  which  it  is  moistened  ;  though  it  is 
also  bathed  with  the  tears  that  spread  out  upon  it,  after 
having  been  conveyed  from  the  eye  through  the  nasal  ducts. 
The  nasal  mucus  seems  as  essential  to  the  sense  of  smell,  as 
the  secretion  from  the  mucous  membrane  of  the  mouth  to 
that-  of  taste.  In  those  who  use  tobacco  in  the  form  of 
snuff,  this  secretion  often  becomes  so  scanty  or  so  changed 
in  quality,  that  the  smell  is  much  impaired,  and  sometimes 
entirely  lost :  the  voice  also  is  seriously  injured  by  the  same 
practice. 

4.  The  olfactory,  or  first  nerve,  is  the  sense  of  smell.  This 
is  spread  out  on  the  thick  vascular  portion  of  membrane  just 
described.  Twigs  from  the  first  and  second  branches  of  the 
fifth,  are  plentifully  ramified  over  the  whole  surface  of  the 
pituitary  membrane,  imparting  to  it  common  sensibility. 
The  nose  is  also  supplied  with  branches  from  the  facial  to 
regulate  the  action  of  the  muscles.  Dr.  Majendie  says,  that 
the  organ  of  smell  ought  to  he  described  as  a  sort  of  sieve^ 
placed  in  the  passage  of  the  air,  as  it  is  introduced  into  the 


180  PHYSIOLOGY. 

chest,  and  intended  to  stop  every  foreign  body  that  may  be 
mixed  with  the  air,  particularly  the  odours. 

5.  What  is  called  odour,  or  smell,  resides  in  nearly  all 
bodies,  and  is  given  off  by  moistwe,  heat,  motion,  or  friction^ 
Those  w^hich  do  not  possess  this  quality  are  called  inodorous. 
Those  little  particles  which  convey  the  odour,  are  scattered 
through  the  air,  and  in  breathing  drawn  into  the  upper  part 
of  the  nostrils,  where  the  sense  of  smell  principally  resides. 
If  we  breathe  through  the  mouth,  odours  in  general  will  not 
be  perceived,  unless  very  pungent.  The  fluid  which  moistens 
the  lining  membrane  of  the  nose,  is  supposed  not  only  to 
render  it  more  sensitive  and  delicate,  but  also  to  entangle 
the  odorous  particles,  and  in  this  way  detain  them  longer  in 
contact  with  the  olfactory  nerve.  The  constant  evaporation 
which  takes  place  from  the  membrane,  owing  to  the  passage  ^ 
of  the  air  in  respiration,  requires  that  the  secretion  shqald 
be  constant  as  well  as  copious ;  otherwise  the  membrane 
would  soon  become  dry  and  parched. 

6.  It  is  very  difficult  to  describe  an  odmr,  except  to  those 
who  have  smelled  it,  or  something  with  which  it  may  be 
compared.  We  can  say  that  odours  are  pleasant  or  dis- 
agreeable  ;  that  they  are  aromatic,  or  smeet,  rancid,  or  fetid, 
&c.  ;  but  we  can  give  no  correct  idea  of  the  peculiar  smell 
of  bodies,  such  as  camphor,  musk,  garlic,  the  rose,  &c.,  with- 
out experiencing  the  sensation  which  their  smell  produces. 

7.  The  odorous  particles  of  bodies  must  be  very  small  to 
excite  any  sensation  on  the  animal  organs.  A  grain  of 
musk  will,  it  is  said,  scent  a  room  for  years,  and  not  lose  any 
of  its  weight  ;  Mr.  Boyle  asserts  that  the  smell  of  cinnamon, 
from  Ceylon,  is  perceived  at  sea  at  the  distance  of  twenty- 
five  miles  from  the  island.  Scales  in  which  a  few  grains  of 
musk  have  been  weighed,  have  been  found  to  retain  the  smell 
for  twenty  years,  though  during  all  this  time,  they  must  have 
been  constantly  giving  off  odorous  particles.  Haller  kept 
some  papers  forty  years,  which  had  been  perfumed  by  a  single 
grain  of  amber,  and  at  the  end  of  that  time  they  did  not 


SENSE    OF    SMELL.  181 

appear  to  have  lost  any  of  their  odour.  But  these  particles 
cannot  be  as  small  as  those  of  light,  because  we  see  that  glass 
is  capable  of  retaining  the  former,  but  suffers  the  latter  to 
pass  through  it.  The  art  of  the  perfumer  consists  in  fixing 
and  preserving  odours  in  the  most  agreeable  and  convenient 
vehicles. 

8.  Odours  differ  very  much  as  to  the  permanence  of  the 
impression  which  they  produce.  While  that  of  some  is  very 
transient,  in  others  the  scent  remains  for  hours  after  the 
application  of  the  substance.  They  also  differ,  as  we  have 
seen,  as  to  the  extent  to  which  their  influence  extends. 
Moisture  in  the  atmosphere  is  favourable  to  the  diffusion  of 
odours,  which  would  seem  to  show  that  vapour  is  a  good 
conductor.  For  example,  a  flower  garden  is  never  more 
grateful  to  the  smell  than  in  the  morning,  when  the  dew  is 
evaporating,  or  after  a  warm  summer  shower.  So  also  the 
plants  of  a  green -house  are  more  fragrant,  just  after  they 
have  been  watered.  Some  flowers  give  ofT  their  odour  only 
at  certain  times,  generally  after  they  are  fully  expanded,  and 
their  parts  in  the  greatest  activity, 

9.  Though  the  air  is  the  usual  vehicle  for  odours,  yet  we 
find  that  they  adhere  to  solid  bodies,  and  can  even  be  con- 
veyed through  water.  But  though  the  whole  art  of  per- 
fumery is  founded  on  this  fact,  it  has  been  strenuously  denied 
that  they  could  be  conducted  through  water,  and  conse- 
quently  that  fishes  could  smell.  Some  physiologists  state 
that  fishes  have  no  olfactory  organ  ;  that  the  part  commonly 
considered  as  such  is  the  organ  of  taste.  This  opinion  is, 
however,  erroneous.  "  Not  many  naturalists  of  the  present 
day,"  says  Dunglison,  "  will  be  hardy  enough  to  deny,  that 
fishes  have  an  organ,  or  sense  of  smell.  ,  At  all  events,  few 
anglers,  who  have  used  their  oil  of  rhodium,  or  other  attrac- 
tive bait,  will  be  disposed  to  give  up  the  results  of  their 
experience,  without  stronger  grounds  than  any  that  have 
been  assigned  by  the  advocates  of  that  view  of  the  subject.'* 

10.  Fishes  are  furnished  with  organs  of  smell,  but  they 

16 


182'  PHYSIOLOGY. 

have  no  communication  with  the  mouth  or  gullet.  They 
are  insulated  cavities,  covered  with  a  valvular  lid,  and  lined 
with  a  plaited  membrane,  similar  to  the  under  surface  of 
some  mushrooms.  This  serves  to  extend  the  suiface,  while 
it  is  covered  with  a  viscid  mucus.  In  the  cod-fish,  the  nerves 
of  smell  are  spread  out  in  a  cavity  filled  with  fluid,  and 
larger  than  that  which  contains  the  brain  itself.  "That  the 
cod  is  guided  by  smell  in  the  selection  of  food,"  says  Aitkin^ 
"must  be  well  known  to  every  one  who  has  taken  it  with> 
bait,  in  circumstances  where  he  could  watch  the  conduct  of 
the  fish.  If  not  very  hungry,  it  may  frequently  be  observed 
to  approach  the  bait,  apparently  attracted  by  the  sight,  till, 
at  a  closer  distance,  it  seems  distinctly  to  smell  at  it ;  and 
if  not  satisfied,  turns  aside  and  neglects  it."  Every  person 
who  has  been  in  the- habit  of  fishing  much,  must  have  often 
observed  the  same  fact,  in  catching  common  pond-fish^  such. 
as  perch,  roach,  &c. 

11.  it  was  an  opinion  formerly  entertained,  that  odours? 
possess  nutritive  properties,  as  savoury  smells  seem  to  have 
the  eflTect  of  allaying  hunger,  or  at  least  of  satisfying  the 
appetite  in  some  degree.  This  effect,  however,  is  best  ex- 
plained, by  referring  it  to  the  influence  of  odours  on  the 
nervous  system,  as  we  see  the  appetite  often  instantly  des, 
troyed  by  unwelcome  news.  In  persons  whose  digestive 
organs  are  weak,  the  appetite  is  often  destroyed  instantane- 
©usly  by  a  nauseous  odour.  We  read  that  Democritus  lived 
three  days  on  the  vapour  of  hot  bread  ;  and  Bacon  speaks 
of  a  man,  who  was  supported  several  days  by  inhaling  the 
odour  of  a  mixture  of  aromatic  and  aliaceous  herbs.  In 
1638,  I>r.  Wilkins,.  the  Bishop  of  Chester,  published  a  book, 
the  object  of  which  was.  to  show  that  the  moon  is  inhabit- 
able, and  that  it  is  possible  for  us  to  find  a  passage  thither. 
In  this  work,  he  says,  "  If  we  must  needs  teed,  upon  some- 
thing, why  may  not  smells  nourish  us  1  Plutarch  and  Pliny, 
and  divers  other  ancients  tell  us  of  a  nation  in  India,  that 
lived  only  upon   pleasing  odours  ;   and  it  is   the  common 


SENSE    OF    SMELL.  183 

opinion  of  physicians,  that  these  do  strangely  botl)  strengthea 
and  repair  the  spirits." 

12.  We  read  an  amusing  anecdote  in  Fuller,  who  lived  at 
the  same  time  with  the  bishop,  in  relation  to  this  supposed 
nourishing  property  of  odours.  A  poor  man  being  very 
hungry,  staid  so  long  in  a  cook's  shop,  who  was  dishing  up 
the  meat,  that  his  stomach  was  satisfied  with  only  the  smell 
thereof.  The  choleric  cook  demanded  of  him  to  pay  for  his 
breakfast;  the  poor  man  denied  having  had  any;  and  the 
controversy  was  referred  to  the  decision  of  the  next  man 
that  should  pass  by,  who  chanced  to  be  the  most  notorious 
idiot  in  the  whole  citj^  ;  he,  on  the  relation  of  the  matter, 
determined  that  the  poor  man's  money  should  be  put  between 
two  .empty  dishes,  and  that  the  cook  should  be  recompensed 
with  the  jingling  of  the  money,*  as  he  was  satisfied  with  the 
cook's  meat. 

13.  The  sense  of  smell  is  closely  associated  with  that  of 
taste.  It  seems  indeed  as  a  sentinel  standing  on  guard,  to 
see  that  no  enemy  approaches  the  citadel  ;  it  tells  us  whether 
the  aliment  placed  before  us,  is  agreeable  or  disagreeable ; 
of  course  whether  it  will  agree  or  disagree  with  the  stomach. 
The  taste  and  the  smell  are  hardly  ever  at  loggerheads ;  it 
does,  however,  sometimes  happen  that  a  substance  that  is  re- 
pugnant to  the  smell,  is  agreeable  to  the  taste.  In  such  a 
case  they  soon  come  to  an  understanding,  and  the  smell 
chooses,  to  make  the  best  of  it,  and  drop  its  repugnance.  At 
any  rate,  its  aversion,  some  way  or  other,  is  soon  neutral- 
ized. The  smell  is,  however  more  useful  to  animals,  as  a 
sentinel,  than  it  is  to  man,  whose  reason  is  more  than  a 
match  for  the  instinct  of  the  brute  creation.  In  them,  in- 
deed, it  rarely  fails  to  guide  ariglit.  How  wonderful  is  this 
provision  which  leads  them  with  unerring  certainty  to  choose 
the  innocent  herb  from  the  poisonous  plant ;  the  nutritious 
vegetable  from  that  which  is  destitute  of  nutriment ;  and  to 

*  Dunglison's  Physiology:. 


184  ,  PHYSIOLOGT. 

reject  instinctively,  every  thing  which  would  prove  noxious 
or  disagreeable.  It  is  not,  however,  infallible  even  in  the 
brute  creation  ;  for  we  see  the  flesh-fly  attracted  by  a  certain 
species  of  mushroom  which  admits  a  cadaverous  odour,  simi- 
lar to  putrid  flesh ;  in  these  they  deposit  their  eggs,  which, 
when  hatched,  perish  for  want  of  suitable  food  to  nourish 
them. 

14.  A  singular  custom,  which  prevails  among  shepherds 
in  some  countries,  shows  that  the  sheep  is  more  under  the 
guidance  of  smell  than  sight  or  any  of  the  other  senses. 
"  When  a  lamb  has  died,"  says  Aitkin,  "  the  shepherd 
wishes  to  put  to  the  ewe  another  lamb  that  may  have  lost  its 
dam  ;  if  she  refuses  to  foster  the  stranger,  he  is  sure  to  suc- 
ceed by  stripping  ofl*  the  skin  of  her  own  offspring,  and  tying 
it  on  the  back  of  the  stranger,  that  she  may  smell  the  skin  ; 
she  then  entertains  and  treats  it  as  her  own.  In  this  case 
she  neglects  the  sense  of  sight,  for  nothing  can  be  more  un- 
couth than  the  object  of  her  affections  ;  neither  does  she 
attend  to  the  evidence  afforded  by  hearing  ;  however  unlike 
the  bleating  of  the  foster  lamb  may  be  to  that  to  which  she 
was  first  accustomed,  her  smelling  is  satisfied,  and  she  is  con- 
tent."    The  same  practice  succeeds  with  the  cow. 

15.  In  the  elephant,  the  tapir,  and  the  hog,  as  well  as  in 
oxen,  sheep,  deer,  and  antelopes,  we  find  the  cavities  of  the 
nose  very  capacious,  and  the  surface  of  the  pituitary  mem- 
brane vastly  extended  ;  and  accordingly  the  sense  of  smell  is 
proportionally  acute.  In  France  it  is  customary  to  employ 
the  hog  to  hunt  for  truffles,  a  species  of  edible  mushroom 
which  grows  at  some  distance  below  the  surface  of  the 
ground.  By  the  sense  of  smell  alone,  he  is  accurately 
guided  to  the  spot  where  one  is  growing,  and  begins  to  turn 
up  the  earth  with  his  snout,  in  order  to  get  at  it.  The  vege- 
table hunter,  however,  anticipates  him,  and  driving  away  the 
animal,  digs  down,  and  appropriates  it  to  himself.  In  this 
way  he  secures,  in  a  short  time,  sufficient  for  a  family  din« 
ner- 


SENSE    OF    STMLELL.  185 

16.  The  delicacy  of  this  sense  in  the  greyhound  is  most 
astonishing.  He  not  only  tracks  the  hare,  the  fox,  or  the 
wolf  with  unerring  certainty,  long  after  their  footsteps  have 
been  imprinted,  but  even  in  a  large  city,  he  will  trace  the 
progress  of  his  master  through  thoroughfares  and  thickly 
crowded  streets,  distinguishing  his  footsteps  from  those  of  a 
thousand  passers-by,  and  amidst  the  odorous  particles  emanat- 
ing from  a  thousand  sources.  When  Hispaniola  was  first  dis- 
covered by  the  Spaniards,  they  employed  the  greyhound  in 
hunting  the  poor  natives,  who,  unlike  the  more  fortunate 
Seminoles  of  Florida,  could  find  no  ever-glade,  no  fastness, 
no  retreat,  which  could  save  them  from  the  unerring  scent 
of  these  animals. 

17.  The  organ  of  smell  is  universally  found  in  birds, 
though  varying  in  size.  Rapacious  birds  and  waders,  or 
those  that  live  on  fish,  have  it  more  largely  developed  than 
any  others.  Humboldt  relates  that  in  South  America,  whea 
the  inhabitants  v/ish  to  take  the  condor,  they  kill  a  horse  or 
cow,  and  in  a  short  time,  the  odour  of  the  dead  animai 
attracts  those  birds  in  great  nunjbers,  and  even  in  places 
where  they  were  scarcely  known  to  exist.  Some  of  the 
Roman  historians  tell  us  that  vultures  went  from  Asia  to  the 
field  of  batUe  at  Pharsalia,  a  distance  of  several  hundred 
miles,  attracted  thither  by  the  smell  of  the  dead.  Pliny,  the 
natural  historian,  affirnis  that  the  vulture  and  the  raven  have 
the  sense  of  smell  so  delicate,  that  they  can  foretell  the  death 
ef  a  man  three  days  beforehand. 

'  18.  Mr.  Audubon,  however,  relates  two  experiments  to 
show  that  vultures  are  indebted  to  sight  rather  than  smell,  in 
the  discovery  of  their  prey.  He  stuffed  a  deer's  skin  with 
hay,  allowed  it  to  become  as  dry  as  leather,  and  placed  it  in  a 
field  ;  in  a  few  minutes  a  vulture  made  for  it,  attacked  it, 
tore  open  the  stitches,  and  pulled  out  the  hay.  He  then  put 
a  dead  hog  into  a  ditch,  and  covered  it  over  with  care  ;  it 
soon  putrefied  and  became  intolerably  offensive,  but  the  vul- 
i^res,  which  were  sailing  about  in  all  directions  in  search  of 

16* 


186  PHYSIOLOGY:. 

food,  never  discovered  it,  although  several  dogs  liad  been 
attracted  to  it  by  the  scent.  His  next  experiment  was  to 
stick  a  young  pig,  and  cover  it  over  with  leaves  ;  vultures 
soon  saw  the  blood,  descended  to  it,  and  by  this  means  soon 
discovered  the  pig,  while  it  was  still  fresh.  The  general 
opinion  of  physiologists  at  present  is,  that  birds  of  prey, 
have  not  so  acute  a  sense  of  smell  as  has  been  generally  sup- 
posed, and  that  they  are  guided  chiefly  by  sight. 

19.  It  is  stated  by  whale-fishermen,  that  in  Greenland, 
when  a  whale  has  been  captured,  although  at  the  time 
scarcely  a  single  bird  may  be  visible^  yet  in  a  short  time, 
immense  numbers  of  gulls  and  other  sea-birds  hover  about, 
and  hasten  to  the  spot  from  every  point  of  the  compass.  Al- 
though these  birds  have  the  organ  of  smell,  and  conse- 
quently the  sense  itself,  largely  developed,  yet  such  facts  may 
be  more  satisfactorily  explained,  than  by  supposing  that  they 
are  able  to  smell  the  flesh  of  a  dead  whale,  before  putrefac- 
tion has  commenced,  at  a  distance  of  many  miles.  A  better 
explanation  cannot  be  given  than  is  contained  in  the  first 
volume  of  "  MacGillivray's  History  of  British  Birds." — 
Speaking  of  ravens  gathering  together  in  immense  numbers 
over  a  dead  carcass,  in  explanation  of  the  phenomenon  he 
remarks,  "  A  single  raven  might  first  perceive  the  carcass. 
Ravens  have  character  in  their  flight  as  men  have  in  their 
walk.  A  poet  sauntering  by  a  river,  a  conchologist  or  fish- 
woman  looking  for  shells  along  the  shore,  a  sportsman 
searching  the  fields,  a  footman  going  on  a  message,  a  lady 
running  home  from  a  shower,  or  a  gentleman  retreatiog 
from  a  mad  bull,  move  each  in  a  different  manner,  suiting: 
the  action  to  the  occasion.  Ravens  do  the  same,  as  well  as 
other  birds  ;  so  those  at  the  next  station,  perhaps  a  mile  dis- 
tant, judging  by  the  flight  of  their  neighbours  that  they  had 
a  prize  in  view,  might  naturally  follow.  In  this  manner  the 
intelligence  might  be  communicated  over  a  large  extent  of 
country,  and  in  a  single  day  a  great  number  might  assemble. 
We  know  from  observation  that  ravens  can  perceive  an 


SENSE    OF    SMELL.  187 

t)bject  at  a  great  distance,  but  that  they  can  smell  food  a 
quarter  of  a  mile  off  we  have  no  proof  whatever  ;  and  as  we 
can  account  for  the  phenomenon  by  their  sight,  it  is  unne- 
cessary to  have  recourse  to  their  other  faculties."  Every 
person  who  has  seen  the  manner  in  which  crows  collect 
together  about  a  dead  animal  in  the  country,  will  be  satis- 
fied that  the  above  is  a  correct  explanation  of  the  pheno- 
menon. 

20.  The  olfactory  organs  of  reptiles  are  but  slightly 
developed.  Frogs  have  two  small  holes,  which  serve  as  the 
organs  of  smell.  The  pituitary  membrane  of  the  turtle  is 
of  a  very  dark  colour,  and  the  nerve  is  of  considerable  size- 
In  serpents,  they  are  more  elongated,  and  in  lizards  still 
more  so.  The  animals  of  this  class  have  no  cavities  corres- 
ponding to  the  sinuses  ;  of  course  the  sense  of  smell  cannot 
be  very  acute. 

21.  The  smell  can  be  greatly  improved  by  education* 
Humboldt  states,  that  the  Peruvian  Indians  can  distinguish 
in  the  middle  of  the  night  the  different  races  by  their  smell ; 
whether  they  are  European,  negro,  or  American  Indian. 
By  habit,  the  perfumer  acquires  the  faculty  of  distinguishing 
the  nicest  shades  of  odours.  We  see  the  influence  of  educa- 
tion, by  the  difference  between  a  dog  that  has  been  trained 
to  the  chase,  and  one  that  has  not.  In  the  blind,  the  sense 
of  smell  is  particularly  acute.  A  boy  in  Edinburgh,  who  was 
born  blind  and  deaf,  could  tell  the  entra  nee  of  a  stranger  in- 
to the  room  by  the  smell  alone  ;  and  he  told  one  person  from 
another  by  smelling  at  him. 

22.  Dr.  Good  remarks,  that  "  we  occasionally  meet  among 
mankind  with  a  sort  of  sensation  altogether  wonderful  and 
inexplicable.  There  are  some  persons  so  peculiarly  affected 
by  the  presence  of  a  particular  object,  that  is  neither  seen, 
tasted,  smelt,  heard,  or  touched,  as  not  only  to  be  conscious 
of  its  presence,  but  to  be  in  agony  till  it  is  removed.  The 
vicinity  of  a  cat  not  unfrequently  produces  such  an  effect ; 
and  I  have  been  a  witness  to  the  most  decisive  proofs  of  this 


188  PHYSIOLOGr. 

in  several  instances."  There  can  be  no  doubt,  I  tlunky  that 
this  peculiarity  is  referable  to  delicacy  of  smell.  Dr.  Dung- 
Hson  states,  that  a  gentleman,  blind  from  birth,  had  an 
extraordinary  antipathy  to  cats.  One  day  in  company,  he 
suddenly  leaped  up,  got  upon  an  elevated  seat,  and  exclaim- 
ed, that  there  was  a  cat  in  the  room,  and  begged  them  to 
remove  it.  It  was  in  vain  that  the  company  assured  him 
that  he  was  mistaken.  He  persisted  in  his  assertion  and  in 
his  state  of  agitation  ;  when,  on  opening  the  door  of  a  small 
closet  in  the  room,  it  was  found  that  a  cat  had  been  acci- 
dentally shut  up  in  it. 


Questions. — Define  the  sense  of  smell.  Where  is  it  seated  ?  De- 
scribe the  pituitary  membrane  ; — the  nose.  What  Savities  are  concern- 
ed  in  the  sense  of  smell  ?  What  is  the  object  of  such  an  extended  sur- 
face ?  How  many  bones  assist  in  forming  the  cavities  of  the  nostrils  ? 
Why  are  they  supplied  with  muscles  ?  Does  the  membrane  that  line 
the  nestrils  resemble  the  other  mucous  membrane  ?  How  is  it  moist- 
ened ?  Do  the  tears  answer  any  purpose  except  washing  the  eye  ? 
What  effect  has  snuff-taki)ig  on  the  sense  of  smell  ?  What  is  the 
nerve  of  smell  ?  What  other  nerves  send  twigs  to  the  nose  ; — their  func- 
tion ?  To  what  does  Majendie  compare  the  organ  of  smell  ?  What 
is  odour  ?  How  given  off  from  bodies  ?  Are  odours  easily  described  ? 
What  facts  show  that  their  particles  are  very  minute  ?  What  is  the 
art  of  perfumery  ?  Do  odours  differ  as  to  the  permanence  of  the  im- 
pression they  produce  ?  What  favours  the  diffusion  of  odours  ?  Can 
odours  be  conveyed  through  water  or  other  flui-ds  ?  Have  fishes  any 
organ  of  smell  ?  What  facts  prove  this  ?  What  article  renders  bait 
attractive  to  fish  ?  Were  odours  ever  believed  to  be  nutritious  ?  What 
anecdotes  in  relation  to  this  ?  Are  the  senses  of  smell  and  taste  asso- 
ciated  ?  What  is  the  use  of  smell?  Are  any  substances  disagreeable 
to  the  smell  and  agreeable  to  the  taste  ?  Is  smell  more  useful  to  ani- 
Kials  than  man  ?  Is  it  infallible  in  them  ?  What  fact  proves  that  it 
is  not  ?  What  singular  custom  prevails  among  shepherds  ?  What 
animals  have  the  sense  of  smell  the  most  acute  ?  How  is  the  smell  of 
the  hog  employed  in  France  ?  What  is  said  of  this  sense  in  the  grey, 
hound  ?  Was  it  ever  employed  to  hunt  savages  ?  When  and  where  ? 
Have  birds  any  organ  of  smell  ?  What  does  Humboldt  say  of  the 
oondor  ?     What  experiments  did  Audabon  try,  to  prove  that  birds  of 


SENSE    01*    SMELL.  189 

prey  are  guided  by  sight  instead  of  smell  ?  What  do  whale  fishermen 
say  of  birds  in  Greenland  ?  How  does  Mr.  MacGilivray  explain  the 
gathering  together  of  so  many  birds  over  a  dead  carcase  ?  Have  rep- 
tiles any  olfactory  organs  ?  Can  this  sense  be  improved  by  education  ? 
What  causes  the  singular  antipathy  to  cats,  which  we  meet  with  in 
some  persons  ? 


CHAPTER  XVL 


THE    SENSE    OF    SIGHT, 


1.  This  is  the  most  refined  and  admirable  of  all  our  senses. 
By  it  especially  we  hold  converse  with  the  external  world  ; 
and  without  it,  we  should  not  only  be  deprived  of  a  large 
portion  of  the  pleasures  we  now  enjoy,  but  we  should  be  un- 
able to  maintain  our  existence  for  anv  length  of  time.  The 
wisdom,  power,  and  benevolence  of  God  are  chiefly  mani- 
fested to  us  through  the  sense  of  vision, 

2.  The  eye  is  the  organ  of  sight,  and  the  most  beautiful 
of  all  the  organs  of  the  senses.  So  admirable  is  its  struc- 
ture, so  wonderful  the  provisions  which  adapt  it  to  the  pur- 
poses for  which  it  was  designed  by  our  Creator,  that  I  shall 
give  as  full  a  description  of  it  as  my  limits  will  allow  ;  and 
in  order  to  an  easy  and  clear  comprehension  of  its  structure 
and  function,  I  shall  first  describe  the  coats  of  the  eye,  in- 
cluding the  retina,  or  the  expansion  of  the  nerve  of  vision ; 
then  the  humours  of  the  eye,  by  the  agency  of  which,  the 
rays  of  light  are  concentrated  so  as  to  form  an  image  upon 
the  retina ;  and  lastly,  explain  the  laws  of  vision,  the  motions 
of  the  eye,  and  the  means  of  protection  against  injury. 

3.  The  Coats  of  the  Eye. — The  coats  of  the  eyeufcre 
generally  reckoned  as  three  in  number,  viz.,  the  sclerotic,  the 
choroid,  and  the  retina ;  besides  these,  there  are  the  cornea, 
the  iris,  and  the  ciliary  processes,  which  are  viewed  and  des- 
cribed as  appendages  to  these  coats. 

4.  The  sclerotic,^  or  outer  coat,  is  the  firm,  opaque,  fibrous 
substance  which  preserves  the  globular  figure  of  the  eye  ;  and 
besides  defending  its  internal  delicate  structure,  serves  for  the 
attachment  of  those  muscles  which  move  the  eye.     It  invests 

*  From  a  Greek  word,  signifying  hard. 


SENSE    OF    SIGHT. 


191 


the  eye  on  every  side  except  the  front,  forming  about  four- 
fifths  of  the  external  covering,  and  extending  from  the 
entrance  of  the  optic  nerve,  at  its  base,  to  the  cornea.  This 
coat  has  almost  the  firmness  of  leather,  and  possessing  but 
little  sensibility,  it  is  rarely  exposed  to  inflammation  or  other 

Fig.  1. 


Plan  of  the  eye,  seen  in  section. 

A,  The  Sclerotic  Coat.  F,  The  Aqueous  Humour. 

B,  The  Choroid  Coat.  G,  The  Iris. 

C,  The  Retina.  H,  The  Ciliary  Processes. 

D,  The  Optic  Nerve.  I,  The  Crystalhne  Lens. 

E,  The  Cornea.  K,  The  Vitreous  Humour. 

dLseases.  The  sclerotic  coat  is  much  denser  in  the  eyes  of 
fishes  than  in  the  eyes  of  creatures  which  live  on  the  surface 
of  the  earth.  In  the  whale,  it  is  more  than  an  inch  thick, 
in  order,,  that  when  he  dives  some  hundreds  of  fathoms  deep, 
the  pressure  of  the  water  on  the  eye  may  not  be  greater  than 
its  structure  can  withstand.  That  this  pressure  is  very  great, 
is  shown  by  the  common  experiment  of  corking  an  empty 
bottle  tigtit,  and  then  letting  it  down  into  the  sea  by  a  cord  ; 
the  cork  will  always  be  found  forced  in,  and  the  bottle  full 
of  water  ;  the  pressure  being  equal  to  the  weight  of  the 
coUnrm  of  water  above  it,  of  which  it  is  the  base.    Dr.  Buck- 


192 


PHYSIOLOGY. 


land  states,  that  in  one  experiment,  a  copper  cylinder,  con- 
taining atmospheric  air,  was  crushed  flat  under  a  pressure 
of  300  fathoms,  and  bottles  filled  with  air  were  crushed  in- 
stantly.  This  shows  the  necessity  of  a  strong  sclerotic  coat 
in  animals  that  dive  far  beneath  the  surface. 

Fig,  2. 


Front  and  side  view  of  the  ball  of  the  eye. 

5.  The  Choroid  Coat,* — This  constitutes  the  second  in- 
vesting membrane  of  the  eye,  which  is  of  a  dark  brown 
colour,  soft,  cellular,  and  vascular.  This  coat  is  situated 
on  the  inner  surface  of  the  sclerotic,  to  which  it  is  slightly 
attached  by  means  of  blood-vessels  and  nerves,  of  which  in- 
deed it  seems  to  be  chiefly  composed  ;  for,  on  injecting  the 
eye  carefully  with  coloured  wax,  it  assumes  a  uniform  red 
colour.  The  inner  as  well  as  outer  surface  of  this  mem- 
brane is  covered  by  the  pigmentum  nigrum,  or  black  paint ;. 
which  seems  to  absorb  the  rays  of  light  immediately  after 
they  have  struck  the  sensible  surface  of  the  retina.  This 
pigment,  sometimes  called  tapetum'\  in  animals  that  see  best 
at  night,  is  wanting  in  albinos,  as  I  have  already  stated  ; 
and  it  is  owing  to  this  cause  that  the  iris  and  pupil  appear 
of  a  red  colour,  and  that  their  vision  is  so  imperfect,  that 
they  cannot  view  objects  in  a  strong  light  ;  and  indeed  can 
scarcely  see  enough  to  go  about  in  the  day-time.  In  ani- 
mals that  prowl  by  night,  this  pigment  is  wanting,  or  of  a 


*  Choroides,  fleecy,  like  a  lamb  skin, 
t  TapetU7ny  like  cloth,  or  tapestry. 


SENSE    OF    SIGHT. 


193 


bright  green,  or  silvery  whiteness,  and  the  dark  pigment  is 
peculiar  to  those  animals  that  see  in  the  brightest  light  of  day. 

Fig,  3. 


The  eye,  after  cutting  away  the  sclerotic  coat  and  cornea,  to  show 
the  vessels  of  the  choroid  coat ;  magnified. 

6.  The  Retina,* — This  is  the  third  and  innermost  mem* 
brane  of  the  eye,  and  is  the  expansion  of  the  optic  nerve, 
and  the  immediate  seat  of  vision.  It  is  a  soft,  thin,  and 
transpai*ent  substance,  extending  from  the  optic  nerve  to  the 
crwalline  lens,  and  lining  the  choroid  coat  throughout  with- 
out whering  firmly  to  it.  The  retina  may  be  divided  into 
threelayers,  viz.,  serous,  nervous,  and  vascular  ;  the  former 
of  whrch  passes  on  over  the  surface  of  the  lens,  and  forms 
part  of  its  capsule.  There  is  a  small  portion  of  the  retina, 
supposed  to  be  near  where  the  optic  nerve  pierces  the 
sclerotic  coat,  which  is  not  susceptible  of  vision,  as  may 
be  shown  by  an  experiment  hereafter  mentioned.  It  was 
formerly  supposed,  that  the  retina  was  endowed  with  extreme 
sensibility  ;  but  it  is  now  ascertained  that  it  is  almost  insen- 
sible to  every  stimulus  but  that  of  light.     The  same  is  true 

*  Retina,  a  net. 
17 


194  PHYSIOLOGY. 

of  the  optic  nerve.  The  ordinary  sensibiUty  of  the  eye  is 
derived  from  the  branches  of  the  fifth  pair  of  nerves  ;  and 
we  have  ah'eady  seen  that  several  pairs  of  nerves  are  sent  to 
its  muscles. 

7.  The  minuteness  with  which  objects  are  painted  on  the 
retina  is  indeed  wonderful.  Standing  on  an  eminence,  the 
eye  takes  in  a  landscape  of  hundreds  of  miles  in  extent ;  and 
all  this  is  painted  on  the  retina,  though,  as  an=  English  writer 
calculates,  a  portion  of  the  castle  of  Edinburgh,  500  Ceet 
long  and  90  feet  high,  occupies  on  the  retina  only  the  twelve 
hundred  thousandth  part  of  an  inch,  when  seen  at  a  certain 
distance.  "  A  whole  printed  sheet  of  newspaper,"  says 
Arnott,  "  may  be  represented  on  the  retina  on  less  surface 
than  that  of  a  finger  nail,  and  yet  not  only  shall  every  word 
and  letter  be  separately  perceivable,  but  even  any  imperfec- 
tion of  a  single  letter  ;  or,  more  wonderful  still,  when  at  night 
an  eye  is  turned  up  to  the  blue  vault  of  heaven,  there  is  por- 
trayed on  the  little  concave  of  the  retina,  the  boundless  con- 
cave of  the  sky,  with  every  object  in  its  just  proportions. 
There  a  moon  in  beautiful  miniature  may  be  saiUng  among 
her  white-edged  clouds,  and  surrounded  by  a  thousand  twink- 
ling stars,  so  that  to  an  animalcule,  supposed  to  be  within 
and  near  the  pupil,  the  retina  might  appear  another  starry 
firmament  with  all  its  glory.  If  the  images  in  the  human 
eye  be  thus  minute,  what  must  they  be  in  the  little  eye^j^f  a 
canary  bird,  or  ofanother  animal  smaller  still !  How  w(rtider- 
ful  are  the  works  of  nature  !"  ^ 

8.  The  Cornea  is  the  term  applied  to  the  anterior  tran- 
sparent portion  of  the  ball.  It  resembles  a  watch  crystal  in 
shape,  and  it  is  received  into  a  groove  in  the  sclerotic  coat, 
in  the  same  manner  as  a  watch-glass  is  received  into  its 
case,  as  in  this  cut.    It  is  somewhat  thicker  than  the  sclerotic 


SENSE    OF  .SIGHT.  195 

coat,  and  is  composed  of  six  concentric  plates  ;  but  its  blood- 
vessels are  so  small,  that  they  exclude  the  red  particles  alto- 
gelher,  and  admit  nothing  but  serum.  Under  the  first  plate, 
little  glands  are  found,  perceptible  only  by  aid  of  the  micro-' 
«cope,  which  are  supposed  to  secrete  an  oil  which  gives  the 
eye  its  bright,  sparkling  appearance.  In  the  last  stage  of 
life,  we  find  this  fluid  forming  a  thin  pellicle  over  the  cornea. 
What  is  called  the  ciliary  ligament,  is  the  groove  or  circle, 
where  the  cornea  is  inserted  in  the  sclerotic  coat. 

9.   We  find  the  tunics  just  described  in  the  lower  grades 
of  animals,  as  well  as  in  man,  differing  of  course  in  form, 
density,  &c.,  but  always  fitted  to  the  circumstances  of  the 
animal.     Thus  in  soft,  molluscous  animals,  the  defensive  coats 
of  the  eye  are  soft  also  ;  but  then  their  eyes  are  placed  on  ten- 
iacula,  or  feelers,  so  that  they  can  retract   them  within  their 
shells.     In  the  articulata,  as  insects,  the  coverings  of  the  eye 
are  firmer,  and  of  a  horny  consistence.    In  the  Crustacea,  such 
a-s  crabs,  lobsters,  &c.,  the  eyes  are  set  in  short  bony  cylinders, 
and  the  cornea  is  often  covered  merely  by  a  portion  of  skin, 
which  passes  over  it.     In  fishes,  we  see  the  cornea  flat,  on 
account  of  the  absence  of  the  aqueous  humour.     In  birds, 
the  cornea  is  conical,  ecrresponding  with  the  quantity  of 
•aqueous  humour  ;  and   it  is  more   prominent  in   rapacious 
birds,  such  as  the  hawk,  eagle,  and  kite,  than  in  aquatic 
birds.     It  is  remarkable  that  the  sclerotica  in  birds  consists 
of  three  different  layers,  the  middle  one  of  which  is  bone, 
and   composed   of  several   plates,   overlapping  each   other  ; 
designed  doubtless  to  protect  their  eyes  against  each  other's 
sharp-pointed  bills,  which  they  have  to  encounter  in  their 
attacks.     In  the  higher  animals,  the  coverings  of  the  eye  are 
similar  to  those  of  man. 

10.  The  Iris,  is  a  circular  membrane,  which  hangs  sus- 
pended  like  a  curtain  in»the  aqueous  humour,  and  is  attach- 
ed to  one  of  the  coats  of  the  eye  at  its  circumference.  It 
derives  its  name  iris,  or  rainboio,  from  the  various  colours  it 
bas  in  different  individuals,  such  as  dark-brown,  pr  black, 


196  PHYSIOLOGY. 

light-grey,  olue,  and  several  shades  and  combinations  of 
these.  It  is  on  this  alone  that  the  colour  of  the  eye  de- 
pends. The  colour  depends  indeed  on  the  refraction  of  the 
light,  as  it  falls  on  the  fleecy  or  velvet-like  surface  of  the 
membrane,  and  also  upon  the  degree  in  which  the  black 
-paint  which  covers  its  back  is  seen  through  it ;  according  as 
the  iris  is  more  or  less  transparent,  will  the  "  colour  of  the 
eye"  be  lighter  or  darker. 

11.  In  many  of  the  lower  animals,  especially  birds,  the 
iris  assumes  a  still  greater  variety  of  colours.  The  round 
hole  in  the  centre  of  the  iris  is  called  the  pupiJf  and  it  is  the 
dark  pigment  of  the  choroid  coat,  that  we  see  througli  this 
when  we  look  into  the  eye  of  another.  Aitkin  says  that  this 
name  has  been  given  to  it,  from  the  fact  that  when  we  look 
into  the  eye,  we  see  a  small  image  of  our  own  face,  like  a 
very  minute  child  or  pupil.  In  albinos,  and  in  animals  that 
see  best  in  the  dark,  like  owls,  the  dark  pigment  is  wanting 
not  only  on  the  choroid  coat,  but  also  on  this  membrane,  and 
as  these  parts  are  very  vascular,  the  blood  is  seen  imparting 
a  red  colour  to  the  eye. 

12.  The  iris  has  the  power  of  dilating  or  contracting  in 
order  to  admit  more  or  less  light  according  as  it  is  needed. 
This  is  effected  by  muscular  fibres.  Of  these,  there  are  two 
kinds.  The  first  set  converge  from  the  circumference  of  the 
iris  to  the  circular  margin  of  the  pupil,  and  are  called  the 
radiated  muscles.  When  these  contract  they  dilate  the  pupil. 
The  other  set  is  composed  of  circular  fibres  which  go  round 
the  border,  and  indeed,  form  the  pupil ;  these  are  called 
the  orbicular  muscle ;  and  when  they  conti*act  diminish  the 
size  of  the  pupil.  Now,  when  more  light  enters  the  eye  than 
is  wanted,  the  excited  retina  immediately  gives  warning  of 
the  danger,  and  the  nerves  which  are  plentifully  distributed 
to  the  iris,  stimulate  the  orbicular  muscle  to  contract,  and 
the  radiated  one  to  relax,  by  which  means  the  size  of  the  pu- 
pil is  instantly  lessened.  On  the  contrary,  when  in  the  dark 
or  twilight,  more  light  is  needed,  to  transmit  a  distinct  image 


SENSE    OF    SIGHT. 


197 


of  objects  to  the  brain,  the  orbicular  muscle  relaxes,  and  the 
radiated  one  contracts,  so  as  to  enlarge  the  pupil  to  its  full 
e^xtent.  Between  these  two  muscles  is  a  middle  layer,  com* 
posed  of  a  net- work  of  blood-vessels  and  nerves. 

Fig.  4. 


I. 


The  cut  marked  I.  represents  the  iris  magnified  as  seen  from  the 
front,  showing  the  radiated  muscle. 

Cut  II.  is  a  back  view  of  the  same  showing  the  orbicular  muscle. 

13.  The  iris  then,  regulates  the  quantity  of  light  passing 
through  the  pupil.  The  pupil  during  sleep  is  in  an  intermediate 
state  ;  in  inflammation  of  the  brain  it  is  generally  contracted  ; 
but  when  the  functions  of  the  brain  are  interrupted  by  nar- 
cotic poisons,  the  pressure  of  effused  fluid,  a  tumour,  or  any 
other  cause,  the  pupil  is  dilated.  The  bella  donna,  or  deadly 
night-shade,  is  employed  by  surgeons  for  this  purpose,  when 
they  wish  to  couch,  or  perform  other  operations  on  the  eye* 
The  contraction  of  the  pupil  is  readily  seen  by  holding  a 
candle  close  to  the  eye  of  a  person,  and  then  withdrawing  it 
slowly  ;  or  by  directing  a  person  to  look  at  a  very  near  ob- 
ject, and  then  at  one  more  distant.  Some  persons  can  dilate 
and  contract  the  iris  at  pleasure.  I  possess  this  faculty  to 
a  very  great  extent,  and  was  conscious  of  it  before  I  ac- 
tually tried  the  experiment.  The  motion  of  the  iris  is  not  at 
all  associated  with  that  of  the  lids,  as  Walker  suggests  in  his 
late  excellent  work  on  the  Philosophy  of  Sight,  the  lids 
remaining  the  whole  time  perfectly  stationary.  I  am,  when 
contracting  the  iris,  sensible  of  an  effort  similar  to  that  of 

examining  a  very  near  object,  and  when  dilating  it,  like  that 

17# 


198  ■    PHYSIOLOGT. 

of  looking  on  one  at  a  distance  ;  but  it  is  not  necessary 
actually  to  look  at  any  object  in  either  case,  nor  do  I  attempt 
it.  If  this  does  not  prove  that  the  muscles  of  the  iris  are 
somewhat  under  the  control  of  the  will,  then  it  cannot  be 
proved  that  any  muscles  of  the  body  are  so. 

14.  The  iris,  in  the  lower  animals,  not  only  presents 
great  diversities  in  colour,  as  has  been  stated,  but  also  in 
form  and  mobiUty.  In  birds,  and  in  the  cat  tribe,  its  mo- 
tions are  free  and  evidently  voluntary ;  but  in  reptiles,  its 
motions  are  obscure  ;  and  in  fishes  imperceptible.  In  rumi- 
nants, in  the  horse,  the  marmot,  in  the  whale  tribe,  and  in 
awls,  the  goose,  and  the  dove  among  birds,  the  pupil  is  elon- 
gated transversely  or  sideways.  In  the  horse,  a  small  square 
curtain  hangs  down,  which  intercepts  a  great  portion  of  the 
rays  coming  from  above.  In  the  cat  tribe,  including  the 
lion,  the  tiger,  leopard,  the  lynx,  the  jaguar,  &;c.  the  pupil  is 
elongated  vertically,  as  it  is  also  in  the  crocodile.  Now  we 
see  a  wise  design  in  this  arrangement,  for  in  such  animals  as 
have  to  watch  their  prey,  which  is  generally  placed  more 
above  them,  as  on  a  tree,  than  at  either  side,  the  pupil  is 
elongated  vertically,  so  as  to  admit  of  more  extended  vision 
in  such  direction  ;  while  in  timid  animals,  like  the  ox,  sheep, 
and  hare,  who  have  to  guard  against  the  insidious  approach 
of  enemies,  while  quietly  grazing  the  fiields,  we  find  this  ar- 
rangement reversed,  and  the  pupil  admits  the  gi'eatest  num- 
ber of  lateral  rays. 

15.  Ciliary  Processes. — These  are  little  folds  or  fringes  of 
thechoroidcoat,  which,  joining  the  sclerotica  near  the  cornea, 
(which  union  is  termed  the  ciliary  ligament)  turn  backwards 
and  inwards,  in  the  form  of  a  circular,  plaited  fringe,  the  lit- 
tle threads  of  which  are  called  the  ciliary  processes.  They 
are  covered,  like  the  choroid,  with  the  black  pigment,  and 
closely  embrace  the  margin  of  the  crystalline  lens,  forming 
round  it  an  opaque  blackened  partition,  which  absorbs  all  the 
side  rays  of  L-ght,  which  might  otherwise  have  disturbed  the 
clearness  of  vision.     These  threads  or  processes  are  plaited 


SENSE    OF    SIGHT.  199 

like  the  folds  of  a  ruffle,  of  which  there  are  about  70  in  the 
human  eye,  all  arranged  in  a  radiated  manner  round  the  lens, 
as  represented  in  the  following  cut. 

Fig.  5. 


Section  of  the  eye  magnified,  showing  the  ciliary  processes,  the  pig- 
mentura  nigrum,  the  retina,  and  the  choroid  eoat. 

16.  The  ciliary  processes  are  thus  cellular  and  vascular, 
and  some  have  thought  muscular,  in  order  to  give  support  to 
the  weight  of  the  crystalline  and  vitreous  bodies,  to  keep 
them  from  falling  towards  the  iris,  or  into  the  aqueous  hu- 
mour. To  accomplish  this,  we  find  them  placed  immme- 
diately  in  front  of  the  vitreous  humour,  and  closely  embrac- 
ing the  circumference  of  the  crystalline  lens,  and  then  to 
strengthen  the  slender  materials  of  which  it  is  formed,  we 
find  it  implanted  in  little  furrows  on  the  surface  of  the  vit- 
reous body,  glued  as  it  were  to  it,  and  adhering  to  it  very 
firmly.  We  know  that  very  substantial  fabrics  are  made  by 
plaiting  and  matting  together  very  slender  and  flimsy  sub- 
stances,  as  straw,  chip,  and  grass  to  form  hats  ;  and  it  is  on 
this  principle,  doubtless,  that  the  ciliary  processes  are  im- 
pacted or  plaited  together. 

17.  Humours  of  the  Eye. — ^The  humours  of  the  eye 


200  "PHYSIOLOGY. 

have  been  compared  to  the  glasses  of  a  telescope,  and  tlie 
coats  to  the  tube  which  keeps  them  in  their  places.  They  are 
three  in  number,  and  though  all  are  perfectly  transparent, 
they  differ  in  density,  and  in  the  space  which  they  respec- 
tively occupy. 

18.  Aqueous  Humour. — The  aqueous  humour  is  as  clear  as 
-the  purest  water,  from  whence  its  name,  although  its  specific 
gravity  is  greater  ;  containing,  as  it  does,  a  little  albumen, 
gelatine,  and  muriate  of  soda.  It  fills  the  entire  space  be- 
tween the  cornea  and  cyrstalline  lens.  The  iris  floats  in  it, 
suspended  like  a  curtain.  The  space  between  the  iris  and 
the  cornea  is  called  the  anterior  chamber  ;  and  that  between 
the  iris  and  the  crystalline  lens,  the  posterior  chamber  of  the 
eye.  This  fluid  is  secreted  by  a  very  thin,  transparent  mem- 
brane which  encloses  it,  though  some  say  it  exhales  from  the 
vessels  of  the  iris,  and  its  chief  office  is  to  distend  the  cor- 
nea, and  preserve  the  iris  in  a  moist  condition,  fit  for  the  dis- 
charge of  its  appropriate  functions.  This  fluid  is  also  in  a 
constant  stale  of  secretion  and  absorption;  for  when 
entirely  discharged,  in  extracting  the  lens,  for  cataract,  we 
find  that  in  a  few  hours  it  will  be  restored  again.  In  old 
age,  its  quantity  is  lessened,  and  the  eye  becomes  flatter, 
needing  the  aid  of  convex  glasses.  Fishes  have  no  aqueous 
humour  at  all,  as  the  water,  in  which  they  swim,  answers  the 
same  purpose,  as  this  was  designed  for,  in  land  animals. 

19.  Besides  this,  the  aqueous  humour  probably  aids  in 
adjusting  the  05^0  to  different  distances.  As  the  lens  lies  im- 
mediately behind  it,  it  is  evident  that,  when  the  quantity  of 
fluid  is  increased,  it  will  press  the  lens  back  nearer  the  re- 
tina, while,  at  the  same  time,  it  renders  the  cornea  more 
convex,  and  the  reverse  happens  when  the  quantity  is  dimi- 
nished. When  the  distension  is  very  great,  the  pressure 
causes  a  cloudiness  or  opacity  of  the  cornea,  thereby  pro- 
ducing blindness.  This  not  unfrequently  happens  with 
horses  that  have  been  fed  during  the  winter  on  dry  food, 
either  placed  on  a  level  with  the  head  or  above  it.     In  the 


SENSE    OF    SIGHT.  201 

spring,  when  they  are  turned  out  to  the  green  pasture,  where 
their  diet  is  changed  from  dry  to  succulent,  and  where  also 
the  head  is  held  near  the  ground  to  collect  the  food,  a  con- 
gestion of  the  aqueous  humour  is  apt  to  occur,  sufficient  to 
produce  temporary  blindness. 

20.  The  Crystalline  Lens. — This  is  placed  immediately 
behind  the  aqueous  humour,  a  short  distance  back  of  the 
pupil,  and  is  a  double  convex  lens,  perfectly  transparent.  In 
shape  it  closely  resembles  the  common  burning  glass  ;  its 
posterior  surface  is,  however,  a  little  more  convex  than  the 
exterior,  and  it  approaches  nearer  to  a  sphere  in  infancy 
than  in  old  age.  When  the  crystalline  lens  is  first  removed 
from  an  eye,  it  looks  like  a  mass  of  transparent  crystal, 
without  any  trace  of  organization.  Near  the  surface  it  is 
much  softer  than  at  the  centre,  which  is  harder  and  more 
compact.  It  is  also  softer  in  the  young  than  in  the  old.  As 
it  consists  chiefly  of  albumen,  when  exposed  to  heat,  as  of 
boiling  water,  alcohol  or  acids,  it  becomes  white,  like  the 
white  of  an  egg.  If  we  examine  it  in  this  state,  we  shall 
find  that  it  consists  of  an  immense  number  of  concentric 
plates  or  Lamella.  More  than  two  thousand  of  these  have 
been  counted,  disposed  in  the  form  of  layers  like  the  coat  of 
an  onion,  each  layer  consisting  of  an  infinite  number  of 
very  minute  filaments,  wound  round  in  diflferent  directions, 
from  various  centres.  The  arrangement  of  these  fibres 
difiers  in  various  animals,  but  is  uniform  in  every  individual 
of  the  same  species.  In  fishes  the  lens  is  nearly  spherical ; 
in  reptiles  it  is  less  so,  and  in  birds  and  mammalia,  it  is  still 
more  flattened.  In  amphibious  animals,  as  turtles  or  frogs, 
or  those  whose  vision  is  adapted  both  for  air  and  water,  as 
seals  and  whales,  the  lens  is  more  convex  than  in  those  which 
live  entirely  in  the  water.  When  this  lens  becomes  so 
opaque  as  to  obstruct  the  passage  of  the  light,  either  par- 
tially or  entirely,  a  person  is  said  to  have  a  cataract.  This 
can  only  be  cured  by  a  surgical  operation. 


202 


PHYSIOLOGY. 
Fig.   6. 


Section  of  the  eye   magnified,  showing  the  Crystalline  Lens  in  its 
proper  situation,  between  the  aqueous  and  vitreous  humours. 


21.  The  Vitreous  Humour. — The  vitreous  ho^y  or  humour 
is  so  called  from  its  resemblance  to  melted  glass.  It  is,  like 
the  other  humours,  perfectly  transparent,  and  occupies  the 
globe  of  the  eye,  of  which  it  constitutes  at  least  the  poste- 
rior two  thirds.  It  is  surrounded  by  the  retina  in  nearly  its 
whole  extent,  to  which,  however,  it  does  not  adhere.  It  is 
composed  of  a  fluid,  contained  in  cells,  formed  of  a  mem- 
brane called  the  hyaloid,  which  communicate  with  each 
other,  so  that  if  it  is  punctured,  the  fluid  with  which  it  is 
filled  will  escape,  though  slowly  in  consequence  of  the  intri- 
cacy of  the  cellular  structure.  On  removing  the  vitreous 
humour  from  the  eye,  it  appears  to  be  of  about  the  consis- 
tency of  the  white  of  an  egg  ;  its  use  being  to  afford  a  sur- 
face for  the  extension  of  the  expanded  retina,  to  keep  the 
lens  at  the  requisite  distance,  and  to  transmit  and  refract  the 
rays  of  light. 


SENSE    OF    SIGHT. 
Fig.  7. 


203 


The  vitreous  humour  and  crystalline  lens  magnified,  with  the  stains 
of  the  pigrnentum  nigrum  left  by  the  ciliary  processes. 

22.  Laws  of  Vision. — Light  passes  through  the  air,  or 
any  mediutn  of  the  same  density,  in  straight  lines ;  but 
when  it  passes  from  one  medium  into  another,  it  is  refracted, 
or  hent  out  of  a  straight  course,  unless  it  strikes  the  new 
medium  in  a  perpendicular  direction,  when  it  passes  directly 
through.  Air,  water,  glass,  or  any  substance  through  which 
light  passes,  is  called  a  medium.  When  a  ray  of  light  passes 
from  a  thinner  or  rarer  medium,  into  one  more  dense,  as 
from  air  into  water,  it  is  bent  towards  a  line  drawn  perpen- 
dicularly to  its  surface.  The  contrary  is  the  case  when  the 
reverse  happens.  This  is  shown  by  plunging  a  straight 
stick  into  the  water,  which  will  appear  crooked.  This  may 
be  illustrated  by  the  familiar  experiment  of  taking  an  object^ 
such  as  a  shilling,  and  fixing  it  at  the  bottom  of  an  empty 
basin,  then  retiring  backwards  until  the  brim  of  the  basin 
hides  it  ;  then  let  water  be  poured  into  the  vessel,  and  the 
coin  will  again  come  to  light,  as  in  the  following  cut.  (See 
Fi^r.  8.) 

TImis  the  ray  of  light  from  the  coin  will  proceed  in  the  di- 
rection a,  previous  to  the  addition  of  the  water,  but  when 
water  is  poured  into  the  vessel,  the  ray  will  be  reflected 
down  to  the  eye,  and  the  shilling  will  appear  to  occupy  the 


204 


PHYSIOLOGY, 

Fig.  8. 


situation  h.  In  the  same  way,  when  we  look  into  a  river, 
the  pebbles  appear  to  be  raised  in  the  water,  and  it  looks 
shallower  than  it  really  is.  From  this  circumstance,  persona 
have  often  been  drowned. 

23.  Lenses.-^A  lens  is  usually  made  of  glass,  its  surface 
being  ground  into  some  of  the  following  shapes  : 

Fig.  9. 


The  first  of  these  on  the  left  hand  would  be  called  a  plain 
lens  ;  the  third,  double  convex  ;  the  fourth,  plano-convex  ;  the 
fifth,  double  concave  ;  the  sixth,  plano-concave ;  the  seventh, 
concavo-convex,  ^c.  Now,  light  in  its  passage  through  these 
glasses,  would  be  refracted  in  proportion  to  their  greater  or 
less  degrees  of  convexity  or  concavity  f  but  in  passing 
through  a  plain  lens,  like  the  first,  the  rays  would  not  be 
bent  out  of  a  straight  course.  For  example,  if  you  place 
an  object  at  the  bottom  of  a  tub  of  water,  and  place  the  eye 
in  a  perpendicular  direction  over  it,  the  object  is  seen  pre- 
cisely in  its  true  situation ;  but  if  you  withdraw  a  short 
distance,  it  will  appear  to  be  situated  where  it  is, not. 


SENSE    OF    SIGHT. 


205 


A,  a  solid  oblong  piece  of  glass  ;  a,  a,  a  stream  of  light,  which 
strikes  the  surface  of  the  glass,  6,  c,  and  which,  being  perpendicular, 
suffers  it  to  pass  through  without  refraction. 

24.  Now  let  us  take  a  concave  lens,  and  see  what  effect 
that  will  have  on  the  light. 


A,  a  solid  oblong  piece  of  glass;  a,  a,  a  stream  of  light  which  strikes 
the  surface  of  the  glass  6,  c,  and  which  being  concave,  causes  the  light 
in  its  passage  through  it  to  diverge. 

25.  Now  try  a  convex  lens,  such  as  the  crystalline  humour 
of  the  eye,  and  see  how  that  will  affect  the  rays  of  light. 


We  see  that  this  form  of  glass  causes  the  rays  of  light 

18 


206 


PHYSIOLOGY, 


a,  a,  to  converge  to  a  point,  or  focus  at  d ;  and  if  it  was  still 
more  convex,  they  would  come  to  a  point  still  nearer.  We 
are  now  able  fully  to  understand  how  it  is  that  the  humours, 
or  lenses  of  the  eye  collect  the  light  from  visible  objects,  and 
converge  them  into  an  image  upon  the  retina.  These  media, 
we  have  seen,  are  four  in  number,  viz.,  the  cornea,  the  aqueous 
humour,  the  crystalline  lens,  and  the  vitreous  humour ;  each 
possessing  a  different  density,  different  sphericity,  and  con- 
sequently different  refractive  powers. 

26.  Now  let  us  examine  the  principle  on  which  an  image 
is  formed.  This  may  be  shown  by  holding  a  common  sun- 
glass opposite  a  window  in  a  room,  and  placing  a  sheet  of 
paper  behind  it.  We  immediately  see  depicted  on  the  paper 
a  perfect  image  of  the  window,  diminished  according  to  the 
eonvexity  of  the  glass,  but  inverted.  The  greater  the  con- 
convexity,  the  nearer  must  the  paper  be  held  to  the  glass  t^^ 
receive  the  image,  and  the  nearer  to  the  window  the  glass  is 
held,  the  larger  will  the  image  appear- 

Fig.  13; 


In  this  cut,  rays  of  light  pass  from  the  candle,  and  the 
hand  A,  B,  and  falling  on  the  lens  at  C,  are  conveyed  to  the 
paper  D,  which  is  consequently  illumined  with  the  object 
in  the  same  way  as  in  the  above  experiment,  the  window 
W£is  painted  on  the  paper*  In  like  manner  precisely,  are 
images  painted  on  the  retina,,  as  is  shown  in  the  following 
eut. 


SENSE    OF    SIGHT. 
Fig.  14. 


207 


27.  Thus  the  convergence  of  the  rays  begins  in  the  aqueous 
humour  is  perfected  in  the  crystalline  ;  but  when  they  strike 
the  vitreous  humour,  which  is  concave  on  its  front  surface, 
and  also  less  dense  than  the  crystalline,  they  diverge  or 
spread  out,  and  are  thrown  upon  the  back  part  of  the  eye. 
The  manner  in  which  this  is  effected  may  easily  be  seen  by 
ithe  following  illustration. 


Fig.  15. 


a,  the  aqueous  ;  c,  the  crystalline  ;  »,  the  vitreous  humour. 

In  passing  through  the  crystalline,  the  rays  cross  each  other, 
so  that  those  rays  which  pass  from  the  lower  part  of  an 
object  are  presented  uppermost  in  the  bottom  of  the  eye  and 
the  reverse,  so  that  the  images  of  objects  are  always  invert- 
ed, or  bottom  side  upwards.  Any  one  can  see  this  by  cut- 
tinff  out  a  circular  portion  of  the  outer  coat,  at  the  back 
part  of  the  eye  of  an  ox  or  sheep  recently  killed,  and  holding 
it  up  at  a  window  ;  he  will  then  see,  on  its  posterior  sur- 
face, a  perfect  but  inverted  representation  of  objects  whether 


208  PHYSIOLOGY. 

stationary  or  in  motion.  Now,  suppose  a  person  was  look- 
ing at  a  church  with  a  tree  standing  at  its  side,  he  would 
have  in  each  eye  an  actual  inverted  panorama  of  the  objects, 
painted  in  a  more  beautiful,  correct,  and  delicate  manner 
than  any  effort  of  art  can  ever  hope  to  exhibit,  as  follows. 

Fig.  16. 


28.  But  if  the  images  of  objects  are  inverted,  why  do  we 
see  things  erect  ?  Locke,  Buffon,  Diderot,  and  other  great 
philosophers,  supposed  that  infants  at  first  see  things  upside 
down,  and  afterwards  learn  to  correct  their  erroneous  sensa- 
tion, by  comparing  the  information  obtained  by  touch  with 
that  acquired  by  sight.  And  not  only  this,  they  maintain- 
ed that  infants  see  every  object  double,  and  all  at  the  same 
distance,  until  experience  corrects  their  errors.  Berkeley, 
however,  contended,  that  we  judge  of  the  position  of  objects 
by  comparing  them  with  our  own  ;  and  as  we  see  ourselves 
as  well  as  every  thing  else  wrong  side  up,  or  inverted,  ex- 
ternal bodies  are  in  the  same  relation  to  us  as  if  they  were 
erect.  But  in  that  case,  the  boy  who  stoops  down  and  looks 
at  objects  between  his  legs,  ought  certainly  to  see  them 
wrong  side  up  ;  but  though  a  little  confused  perhaps  at  first, 
he  soon  sees  in  that  way  as  well  as  any  other.  This  diffi- 
culty is  easily  explained  by  what  is  called  the  law  of  visible 
direction  ;  that  is,  each  point  of  an  object  is  seen  perpendi- 
cular to  the  point  of  the  retina  on  which  its  image  falls. 
The  surface  of  the  retina  being  concave,  and  nearly  as  poa- 


SENSE    OF    SIGHT.  209 

4sible  splierical,  these  lines  of  visible  direction  meet  and  cross 
at  a  point  within  the  eye,  which  is  called  the  centre  of  visible 
direction  ;  the  lines  from  the  upper  part  of  the  image  go  to 
the  lower  part  of  the  object,  and  those  from  the  lower  part 
of  the  image  proceed  to  the  upper  part  of  the  object.  Thus 
an  inverted  image  necessarily  produces  an  erect  object,  and 
the  external  object  is  the  thing  to  which  the  mind  attends, 
and  not  the  object  on  the  retina.  The  error  of  all  these 
philosophers  has  consisted  in  this,  that  they  have  imagined 
a  true  picture  to  be  formed  on  the  retina,  which  is  regarded 
by  the  mind,  and  therefore  seen  inverted.  But  there  is  no 
interior  eye  to  see  or  take  cognizance  of  this  image  ;  but 
the  mind  accurately  refers  the  impression  made  on  the 
retina  to  the  object  producing  it.  In  short,  the  mind  stands 
behind  the  retina  and  looks  at  objects  as  they  are  through 
this  screen,  but  it  does  not  see  the  screen  itself,  but  judges 
of  the  position  of  objects  by  the  direction  in  which  the  light 
comes  from  them  towards  the  eye  ;  and  as  Arnott  well 
remarks, — "  no  more  deems  an  object  to  be  placed  low  be- 
cause its  image  may  be  low  in  the  eye,  than  a  man  in  a 
room  into  which  a  sun-beam  enters  by  a  hole  in  the  window- 
shutter,  deems  the  sun  low  because  its  image  is  on  the 
floor," 

29.  Again,  why,  as  we  have  two  eyes,  does  not  every 
object  appear  double  ?  The  reason  is,  that  in  the  two  eyes 
are  corresponding  points,  so  that  when  a  similar  impres- 
sion is  made  on  both,  the  sensation,  or  vision,  is  single. 
Now,  we  have  the  faculty  of  so  directing  the  axis  of  the 
eyes,  that  the  image  of  an  object  falls  exactly  on  the  same 
point  in  each  ;  but  if  from  any  cause  there  is  the  least  dis- 
turbance, then  vision  becomes  double,  as  often  happens  to 
the  drunkard.  This  is  easily  known  by  slightly  pressing 
a  finger  on  the  ball  of  either  eye,  so  as  to  prevent  its  following 
the  motion  of  the  other.  Persons  who  squint  always  have 
double  vision,  but  then  they  acquire  the  power  of  attending 
to  the  sensation  in  one  eye  at  a  time.     Animals  that  have 

18* 


210  PHYSIOLOGY. 

the  eyes  placed  on  opposite  sides  of  the  head,  possess  in  a 
more  remarkable  degree  the  faculty  of  thus  attending  to  one 
thing  at  a  time» 

30.  It  follows  then,  that  the  eye  itself  does  not  see  ;  it  is 
only  an  instrument  employed  by  the  brain,  or  rather  the 
mind,  whose  servant  the  brain  is.  The  optic  nerve  is  the 
channel  by  which  the  mind  peruses  the  hand  writing  of  na- 
ture on  the  retina,  and  through  which  it  transfers  to  that 
material  tablet  its  decisions  and  its  creations.  There  is  then 
a  portion,  or  rather  an  argan  of  the  brain,  where  vision  or 
VaQ^nincVs  eye  is  seated  ;  and  this  portion  is  sometimes  im- 
perfectly constituted  or  organized,  as  Gall  has  proved  to  be 
the  case,  in  those  who  cannot  distinguish  colours.  That 
such  is  a  true  statement  of  facts,  we  learn  from  observing  that 
disease  of  a  given  portion  of  brain  produces  blindness,  whilst 
the  eye  remains  perfectly  healthy.  Either  this  was  the  case 
with  Milton,  or  he  was  afflicted  with  amaurosis,  or  palsy  of 
the  retina,  for  he  says, 

"  These  eyes,  though  clear 
To  outward  view,  of  blemish,  or  of  spot, 
'  -.  Bereft  of  light,  their  seeing  have  forgot ' 

Nor  to  their  idle  orbs  doth  sight  appear 
Of  sun,  or  moon,  or  star  throughout  the  year !" 

We  also  have  the  power  of  internal  vision  when  asleep  ;  and 
those  who  have  lost  their  eyes  perceive  spectral  illusions,  and 
other  similar  phenomena,  and  they  can  also  conjure  up  the 
figures  and  forms  of  various  objects  familiar  to  them  before 
they  lost  their  vision. 

31.  From  the  principles  now  laid  down  we  can  understand 
why  rivers  appear  shallower  than  they  are,  and  why  a  stick 
placed  in  the  water  appears  crooked.  In  spearing  of  fish, 
or  shooting  them  in  the  water,  every  sportsman  knows  that 
he  must  make  suitable  allowance  for  this  refraction,  for  the  fish 
is  always  nearer  to  him  than  it  appears.  Birds  that  dive  for 
fish  seem  to  understand  that  there  is  but  small  chance  of 
success  if  they  dive  obliquely  into  the  water,  so  like  skilful 


SENSE    OF    SIGHT. 


211 


opticians,  they  hover  over,  and  when  they  see  their  prey, 
dart  down  perpendicularly,  in  which  direction,  as  we  have 
seen,  there  is  no  refraction.  There  is  a  curious  fish  in  the 
East  India  waters  called  chactodon,  about  eight  inches  long, 
that  appears  to  understand  optics  remarkably  well.  When 
it  sees  a  fly,  sitting  on  the  plants  that  grow  in  shallow  water, 
it  swims  within  five  or  six  feet,  and  then  with  the  dexterity 
of  a  practical  marksman,  ejects  from  its  tubular  mouth  a 
single  drop  of  water  which  never  fails  to  strike  the  fly  into 
the  sea,  where  it  soon  becomes  its  prey.  Dunglison  states 
that  Hommel,  the  Dutch  governor,  put  some  of  these  fish 
into  a  tub  of  water,  and  then  pinned  a  fly  on  a  stick  within 
their  reach.  He  daily  saw  the  fish  shoot  at  the  fly,  and  they 
Hever  failed  to  hit  their  mark. 

32.  Short-sightedness. — This  generally  arises  from  too 
great  convexity  of  the  cornea,  or  excessive  density  in  the 
structure  of  the  crystalline  lens ;  either  of  which  will  cause 
the  visual  rays  from  near  objects,  to  converge  to  a  focus,  be- 
fore they  reach  the  retina.  This  is  remedied  by  concave 
glasses,  which,  as  we  have  seen,  cause  the  rays  to  diverge,  as 
is  represented  in  the  following  cut. 

Fig.  17. 


A.  a  short-sighted  eye ;  B.  an  arrow  which  it  attempts  to  perceive,, 
but  is  prevented  by  the  convergence  of  the  passage  of  the  visual  ra}'* 
to  focij  at  C,  before  they  reach  the  retina  at  D.     E.  the  same  eye. 


212  PHYSIOLOGY. 

similarly  situated,  showing  how  by  the  intervention  of  a  concave  lens, 
G.,  the  rays  are  di-verged,  and  the  image  of  the  arrow,  F.,  accurately 
converged  to  the  retina  at  A. 

33.  Long-sightedness  is  the  opposite  defect  to  this,  and  is 
owing  to  a  flattening  of  the  cornea,  and  a  relaxation  in  the 
structure  of  the  crystalline  lens,  by  which  its  power  of  re- 
fraction is  lessened.  In  this  case,  the  rays  of  light  are  car- 
ried beyond  the  retina,  and  therefore  do  not  form  a  distinct 
image  on  it.  Old  persons  usually  are  subject  to  this  defect ; 
the  only  remedy  known  is  convex  glasses.  Where  persons 
have  been  short-sighted  in  youth,  as  the  eye  grows  flatter  by 
age,  they  at  length  are  able  to  see  well,  without  glasses  of  any 
kind.  This  change  in  the  shape  of  the  eye  is  often  denoted 
hy  a  tendency  to  hold  a  book  at  a  greater  distance  when 
reading.  Grlasses  do  for  the  eye  that  portion  of  the  labour 
of  bending  the  rays  of  light,  which  it  is  not  able  to  do  for 
itself.  By  adapting  glasses  to  the  successive  changes  which 
age  produces  in  the  shape  of  the  eye,  the  sight  may  be  pro. 
longed  very  often  to  the  close  of  life.  After  the  operation  of 
extracting  the  crystalline  lens  for  cataract,  or  depressing  it 
by  couching,  very  convex  glasses  are  needed  to  remedy  the 
deficiency. 

34.  The  sight  is  often  injured  by  long-protracted  attention 
to  minute  and  near  objects  ;  as  we  see  in  the  watch-maker 
and  engraver ;  also  by  watching  for  objects  at  a  distance ; 
as  in  sailors,  and  keepers  of  telegraph  stations ;  in  the  one 
case  the  eye  becoming  near,  and  in  the  other  far-sighted. 
During  the  arbitrary  reign  of  Napoleon,  the  young  men  of 
France  often  produced  short-sightedness  voluntarily,  by  wear- 
ing  very  concave  glasses,  in  order  that  they  might  be  exempt 
from  military  service. 

35.  Some  persons  are  unable  to  tell  one  colour  from 
another.  Sir  David  Brewster  gives  us  the  following  exam- 
ples. A  Mr.  Scott  mistook  pink  for  pale  bluCf  and  red  for 
green.  His  father,  uncle,  sister,  and  two  sons,  all  mistook 
these  colours  in  the  same  way.     A  shoemaker  named  White, 


SENSE    OP    SIGHT.  213 

could  only  see  two  colours,  black  and  white,  and  he  could 
never  distinffuish  the  cherries  on  a  tree  from  the  leaves.  A 
tailor  at  Plymouth  could  only  see  yellow  and  hliie.  On  one 
occasion  he  repaired  a  hlack  silk  garment  with  crimson,  and 
on  another,  he  patched  the  elbow  of  a  blue  coat  with  a  piece 
of  red  cloth.  M.  Nicoil  tells  us  of  an  officer  in  the  British 
navy,  who  purchased  a  blue  uniform  coat  and  waistcoat, 
with  red  breeches  to  match.  The  cause  of  this  defect  is 
believed  to  be  a  malformation,  or  deficiency  of  that  portion 
of  the  brain  which  takes  cognizance  of  colours. 

36.  The  lowest  order  of  animals  have  no  organs  of 
vision,  or  if  so,  they  have  never  been  detected.  Many  in- 
sects have  two  kinds  of  eyes,  one  kind  on  each  side  of  the 
head,  and  the  other  on  the  top,  in  a  row,  or  in  the  form  of  a 
triangle.  The  spider  has  generally  eight  of  these  eyes  on 
the  top  of  the  head.  What  are  called  the  compound  eyes 
are  placed  on  the  side  of  the  head,  and  in  the  wasp  and 
dragon-jiy  they  covei'  a  large  part  of  it.  These  eyes  are 
formed  of  a  large  number  of  separate  cones  or  cylinders, 
closely  packed  together,  each  being  a  distinct  eye,  and  hex- 
agonal, or  six-sided  in  shape,  like  the  cells  of  a  honey-comb. 
The  ant  has  about  50  ;  the  beetle  3,000  ;  the  silk-worm  moth 
upwards  of  6,000  ;  the  dragon-fly  12,000  ;  and  some  in- 
sects as  many  as  20,000. 

37.  It  is  now  ascertained,  that  each  eye  forming  these 
compound  eyes  of  insects,  consist  of  a  distinct  tube,  furnished 
with  every  thing  necessary  for  complete  vision.  The  object 
of  this  wonderful  arrangement  seems  to  be  to  compensate  for 
want  of  motion,  by  the  number  of  eyes,  as  the  insect  thus 
supplied,  has  an  eye  pointed  tosvards  the  object  in  whatever 
direction  it  may  appear,  and  may  therefore  be  truly  called 
circumspect.  If  we  examine  the  wasp  and  dragon-fly,  we 
shall  find  these  compound  eyes  to  cover  a  large  portion  of 
each  side  of  the  head.  By  examining  with  the  microscope, 
we  find  each  of  these  conical  tubes  covered  with  a  cornea, 
and  containing  a  crystalline  lens,  and  aqueous  and  vitreous 


214  PHYSIOLOGY. 

humour,  an  iris,  a  choroid  coat,  and  a  retina ;  the  pigment 
running  back  around  the  lens,  separating  each  cyUndrical 
compartment.  They  have  no  eye-Uds,  eye-lashes,  or  tears  ; 
but  these  are  compensated  for  by  the  great  hardness  and  in- 
sensibility of  the  cornea. 

Fig.  18. 


Eye  of  the  yellow  beetle  magnified,  composed  of  8,820  hexagoneU 
cylinders,  the  interior  of  each  tube  being  round. 

Fig.  19. 


Eye  of  the  phalaena  or  butterfly,  magnified,  consisting  of  11,300 
square  sections.  The  eye  of  the  mordella  is  similar,  containing  25,088 
prisms. 

38.  Motions  of  the  Eye. — We  have  seen  that  the  eye  is  a 
perfect  optical  instrument,  infinitely  surpassing  the  boasted 
specimens  of  human  skill ;  but  without  the  power  of  motion, 
of  adapting  it  to  the  varied  objects  which  surround  us,  we 
should  derive  but  a  very  small  proportion  of  that  gratification 
and  pleasure,  of  which  it  is  now  the  source.  We  shall  per- 
ceive the  great  advantages  we  enjoy  from  this  benevolent 
provision,  if  we  contemplate  the  movements  of  a  telescope  ; 
how  difficult  it  is  to  direct  it  to  any  object,  so  as  to  obtain  a 
view  of  it,  and  what  complicated  and  cumbrous  machinery 
are  required  to  effect  it.  But  all  the  various  motions  of  the 
eye  are  produced  by  six  little  muscles  ! 


SENSE    OF    SIGHT.  215 

39.  Four  of  the  muscles  of  the  eye  are  called  straight  or 
recti  muscles  ;  the  other  two  are  named  the  oblique  muscles. 
The  first  four  arise  from  the  back  part  of  the  orbit,  and  are 
inserted  by  broad  thin  tendons  into  the  four  sides  of  the 
globes  near  the  junction  of  the  cornea  with  the  sclerotic 
coat.  The  white  pearly  appearance  of  the  eye  is  caused  by 
these  tendons.  The  oblique  muscles  arise  from  the  front  and 
inner  side  of  the  orbit,  and  pass  to  the  eye-ball  at  right  angles 
from  the  straight  muscles,  one  passing  over  its  upper  surface^ 
and  the  other  upon  its  under  surface,  and  both  are  inserted 
into  its  outer  side,  one  a  little  above  its  horizontal  axis,  the 
other  a  little  below  it.  The  superior  oblique  muscle  is,  how- 
ever, worthy  of  more  particular  notice,  as  no  part  of  the 
body  exhibits  clearer  marks  of  design  and  contrivance.  It 
arises  as  I  have  said,  from  the  bottom  of  the  orbit,  it  proceeds 
forwards  and  becomes  tendinous,  and  when  it  reaches  near 
the  margin  of  the  oi'bit,  it  passes  through  a  little  cartilagi- 
nous pulley,^  by  which  the  direction  of  its  action  is  changed, 
precisely  as  we  see  done  by  a  pulley  among  the  ropes  of  a 
ship  ;  after  passing  through  this  little  loop,  which  is  dense, 
smooth,  and  elastic,  and  furnished  with  a  lubricating  fluid  to 
diminish  friction,  the  tendon  runs  obliquely  backwards  and 
towards  the  internal  angle  to  be  inserted  into  the  ball.  When 
this  muscle  acts,  the  eye  is  rolled  directly  inwards.  Thus 
the  muscle  pulls  in  a  direction  contrary  to  its  own  action,  as 
when  a  man  raises  himself  by  a  rope  thrown  over  a  beam» 
The  other,  or  inferior  oblique  muscle,  rolls  the  eye  outwards- 
towards  the  temple.  When  they  both  act  together,  the  eye 
is  steadily  carried  forwards.  The  recti  muscles  move  the 
eye  in  four  directions,  upwai*ds,  downwards,  to  the  right,  and 
to  the  left,  each  movement  being  affected  by  its  appropriate 
muscle.  When  the  four  act  together,  the  eye  is  drawn  back 
towards  the  bottom  of  the  orbit. 


216 


PHYSIOLOGY. 
Fig.  20 


Side  view  of  the  muscles  of  the  eye  in  their  natural  positions,  a.  h. 
C,  d.  the  four  straight  muscles,  a.  is  turned  up  to  prevent  the  others 
from  being  hidden,  e.  the  superior  oblique  muscle.  /.  the  optic  nerve. 
The  other  oblique  muscle  is  not  shown,  but  it  lies  on  the  other  side  of 
the  ball,  and  comes  round,  and  is  inserted  near  the  superior  oblique  ;  so 
that  they  pull  opposite  ways,  like  two  men  sawing  timber.  By  the  com- 
bined action  of  all  these  muscles,  an  infinite  variety  of  motions  of  the 
eye  can  be  produced. 

40.  In  order  to  facilitate  the  motions  of  the  eye  it  is 
lodged  securely  on  a  soft  bed  of  fat.  This  is  contained  in 
very  large  cells  at  the  bottom  of  the  orbits,  and  is  more 
fluid  than  fat  in  general,  and  is  less  affected  than  any  other 
part  of  the  body  by  those  causes,  which  produce  general 
emaciation.  The  eye-ball  may  therefore  be  said  to  move  in 
a  fluid  medium,  fully  adequate  to  give  every  necessary  sup- 
port, and  at  the  same  time  affording  the  least  possible  resist- 
ance. 

41.  Defences    and  Appendages  of  the   Eye. — These  are 


SENSE    OF    SIGHT.  217 

the  orbit,  the  eyebrows,  the  eyelashes,  the  eyelids,  and  the 
lachrymal  ajoj^aratus.  The  orbit  is  a  four-sided  vault,  com- 
posed of  seven  bones,  and  shaped  Uke  a  pyramid  or  cone, 
the  apex  pointing  backwards.  The  eyeball  and  the  orbit 
seem  exactly  made  for  each  other ;  the  one  being  globular, 
the  other  rounded  to  receive  it.  At  the  bottom  of  the  orbit 
are  holes  for  the  passage  of  the  blood-vessels  and  nerves. 
Now  this  cavity  is  not  scooped  out  of  the  skull,  as  a  boy 
would  make  a  hole  in  a  block  of  wood,  but  the  seven  bones, 
which  enter  into  its  composition,  are  so  curiously  dove-tailed 
together  as  just  to  leave  this  space  for  the  reception  of  the 
eye  and  its  appendages.  What  mechanic  could  place 
seven  irregular,  jagged  bones  together  so  as  to  form  a  smooth, 
polished  cavity,  for  such  a  delicate  organ  as  the  eye  to  roll 
iji  !  So  securely  is  the  eye  protected  by  its  bony  house  or 
encasement,  that  it  is  a  very  rare  thing  for  it  to  be  injured, 
except  by  some  sharp  pointed  object. 

42.  The  eye  then  is  surrounded  on  every  side  with  bone, 
except  the  front ;  now,  what  have  we  here  to  serve  as  a 
means  of  defence  ?  It  would  not  have  answered  our  pur- 
pose to  have  had  it  entirely  shut  up  in  a  box  of  bones,  or 
even  to  have  left  a  little  hole  just  to  peep  through.  As  we 
cannot  draw  our  heads  into  a  shell  when  danger  threatens, 
like  a  snail  or  turtle,  we  are  furnished  with  a  couple  of 
moveable  curtains  or  eyelids,  placed  before  the  eyes,  which 
we  can  let  down  or  raise  up  just  when  we  please.  If  the 
eyes  are  "the  windows  of  the  soul,"  then  I  would  call  the 
lids  a  pair  of  inimitable  window  shutters,  for  they  exclude 
the  light  whenever  its  presence  would  be  disagreeable  to  ua. 

43.  The  eyelids  are  composed  of  a  thin  skin,  externally; 
internally  of  cellular  membrane, — its  cells  filled  with  a  soft 
semi-transparent  fluid  ;  while  their  inner  surface,  in  contact 
with  the  eye,  is  lined  with  a  delicate  mucous  membrane, 
continuous  with  the  skin,  called  conjunctiva.  Besides  these 
there  are  beneath  the  skin,  two  sets  of  muscular  fibres;  one 
called  orbicular,  running  round   the  lid  horizontally,  whose 

19 


218  PHYSIOLOGY. 

contraction  serves  to  close  the  eye  ;  the  other  lying  beneath, 
are  the  fibres  af  the  levator  muscle,  which  serves  to  raise  the 
Kd,  or  open  the  eye.  These  two  muscles  are  well  exhibited 
in  the  following  cut : 

Fig.  21. 


Muscles  of  the  eyelids^,  the  elevator  passing  back  into  the  orlHt ;  the 
sphincter,  or  orbicular  muscle  surrounding  the  eye. 

44.  Around  the  margin  of  each  lid,  there  is  a  delicate 
elastic  cartilage  placed,  which  serves-  to  preserve  the  shape 
©f  the  lid  ;  and  into  this,  £ts  is  showct  in  the  cut,  the  fibres 
ef  the  elevator  muscle,  are  inserted.  In  contact  and  around 
each  cartilage,  on  its  anterior  surface,  at  the  root  of  the  eye- 
lashes, is  situated  a  row  of  little  bags  or  follicles,  which 
secrete  an  oily  fluid,  to  keep  the  parts  soft  and  pliant,  and 
prevent  the  lids  from  sticking  together.  It  is  this  matter 
which  we  often  find  in  the  morning,  collected  on  the  margin 
©f  the  lids,  or  in  the  internal  angle  of  the  eye. 

45.  Now,  mark  this  difierence  ;  the  levator  muscle,  which 
lises  from  the  bottom  of  the  orbit,  is  entirely  under  the  con- 
trol of  the  will ;  the  orbicular  muscle  is  not.  See  the  ad- 
vantage of  this.  If  we  had  always  to  issue  a  command  of 
the  will  to  shut  the  eyes,  before  going  to  sleep,  I  imagine 
there  are  a  good  many  in  this  lazy  world  who  would  foYgQt 
to  shut  their  eyes,  and  so  go  ta  sleep  with  them  wide  open. 
To  what  dangers  would  they  be  exposed,  and  what  injuries 
might  they  not  sustain   in    consequence!      But   watch   a 


SENSE    OF    SIGHT.  219 

sleepy  person.  No  sooner  does  he  begin  to  grow  drowsy, 
than  his  eyes  begin  to  close ;  in  other  words,  "  they  grow 
heavy."  If  he  wishes  to  keep  awake  he  makes  a  desperate  ef- 
fort to  open  his  lids  ;  and  in  the  drunkard,  whose  involuntary 
muscles  overpower  the  voluntary  ones,  it  is  quite  ludicrous  to 
watch  the  expression  of  countenance,  and  see  how  quick  the 
disobedient,  rebel  lids  close,  upon  the  oft-repeated  efforts  to 
keep  them  open. 

46.  The  opening  and  closure  of  the  lids  ordinarily  occu- 
pies about  the  eighth  part  of  a  second,  so  that  there  is  no 
interruption  to  the  continuance  of  vision.  Besides  serving 
as  a  curtain  to  protect  the  eye,  the  lids  serve,  by  their  mo- 
tions to  diffuse  the  tears  and  mucous  secretions,  thus  keep- 
ing the  surface  of  the  cornea  moist,  and  wiping  off  any 
foreig^n  matter,  as  dust,  that  may  be  lodged  on  it.  The  eye- 
lids when  closed,  do  not  entirely  prevent  the  transmission  of 
light ;  for  when  we  have  been  refreshed  by  sleep,  the  stimulus 
of  the  light  falling  upon  the  lids,  is  sufficient  to  arouse  sen- 
-sibility  and  awake  us. 

47.  It  is  a  curious  fact,  that  while  the  upper  eye-lid  falls, 
the  lower  eye-lid  is  moved  towards  the  nose,  and  thus  aids 
in  collecting  all  offensive  particles  in  the  corner  of  the  eye. 
This  can  readily  be  shown  by  marking  the  edges  of  the  lids 
with  a  black  spot ;  when  the  lids  are  opened  and  closed,  the 
spot  on  the  upper  eye-lid  will  rise  and  fall  perpendicularly, 
while  that  on  the  lower  one  will  play  horizontally  like  a 
weaver's  shuttle.  When  any  thing  gets  into  the  eye,  there 
IS  this  continual  play  of  the  lids  maintained,  till  the  offend- 
ing particles  have  been  driven  into  the  inner  corner  of  the 
eye,  when  relief  is  at  once  obtained.  When  the  object  is 
very  small,  or  not  sufficiently  irritating  to  excite  these 
muscles  of  the  lids  to  action,  it  is  common  to  place  an  eye- 
stone,  which  is  a  smooth  piece  of  sulphate  of  lime  in  the 
eye.  This  not  only  excites  an  abundant  secretion  of  tears, 
but  also  causes  the  necessary  motions  of  the  lids,  by  which 
the  object  is  soon  washed  into  the  angle  of  the  eye. 


220  PHYSIOLOGY. 

48.  Maoy  animals  have  what  may  be  called  a  third  eye- 
lid, called  the  nicitating  membrane.  This  slides  from  one 
angle  of  the  eye  to  the  opposite  side,  under  the  lids,  whether 
open  or  shut.  Its  use  is  to  clear  away  all  matter  which 
might  be  irritating  to  the  eye.  Birds  that  see  best  by  night, 
such  as  owls,  defend  their  eyes  against  the  light  of  the  sun, 
by  drawing  this  curtain  over  them. 

49.  The  eye-lashes,  or  cilia,  also  aid  in  the  protection  of 
the  eye.  They  ward  off  insects,  protect  the  eye  from  par- 
ticles floating  in  the  air,  and  also  break  the  intensity  of  light. 
Indeed,  when  moist,  as  they  often  are  with  perspiration,  the 
little  drops,  serve  to  decompose  the  rays  of  light,  causing  the 
appearance  of  a  luminous  zone  around  the  flame  of  a  candle. 
The  eye-brows  are  composed  of  loose  cellular  substance, 
covered  with  skin,  from  which  spring  short  bristly  hairs 
projecting  outwards.  Like  all  hairs,  they  penetrate  little 
follicles,  and  become  besmeared  with  an  oily  secretion,  which 
preserves  their  glossiness,  so  that  the  drops  of  sweat  which 
may  accumulate  on  the  brow  are  prevented  from  trickling 
over  the  eye-lids,  where  they  might  interfere  with  vision. 

50.  J^achrymal  Apparatus. — The  tears-  are  secreted  by  the 
lachrymal  gland,,  which  is  a  small  spongy  body  of  a  flatten- 
ed form,  seated  in  the  hollow  of  the  bone,  in  the  upper  and 
outer  part  of  the  orbit,  just  beneath  the  outer  end  of  the 
bone.  These  serve  as  fountains,  as  well  as  laboratories  or 
distilleries,  separating,  as  they  do,  a  pure  water  from  the  red 
blood,  and  discharging  it  by  means  of  seven  or  ei^ht  little 
tubes,  upon  the  inner  surface  of  the  upper  eye-lid,  from 
whence  it  is  spread  along  with  the  mucus  from  the  con- 
junctiva over  the  eye,  by  the  movements  of  the  lids.  But 
what  becomes  of  the  tears  ?  In  the  inner  corner  of  the  eye 
are  two  very  minute  apertures,  one  in  each  lid,  which  are 
the  orifices  of  two  canals,  which  communicate  with  a  pipe, 
by  which  the  superfluous  moisture  is  drained  off*  into  the 
nostrils.  This  process  is  constantly  going  on  without  notice. 
But  when  there  is  much  irritation,  then  the  natural  chan- 


SENSE    OF    SIGHT. 


221 


iiels  are  insufficient  for  their  escape,  and  the  tears  roll  over 
the  cheek. 

Fig.  22. 


a,  the  eye-ball,  and  b,  b,  are  the  upper  and  lower  sides.  Now  in  order 
to  prevent  dust  and  other  bodies  from  working  their  way  between  the 
Dall  and  the  lid,  through  passages  at  e,  e,  into  the  socket  of  the  eye, 
where  they  would  excite  great  inconvenience  and  pain,  we  find  the 
common  skin  of  the  eye-lids  d,  d,  after  covering  their  edges,  turn  in  a 
little  way  between  the  lid  and  the  ball,  and  then  turn  back  and  are 
reflected  over  the  surface  of  the  cornea  ;  where,  to  prevent  the  obstruc- 
tion of  vision,  it  becomes  perfectly  transparent, 

Fig.23> 


The  eye-lids  separated,  and  viewed  from  behind  ;  a,  the  lachrymal 
gland  ;  b,  the  ducts  from  the  lachrymal  gland  ;  c,  the  mouths  of  these 
ducts  ;  d,  the  puncta  lachrymalia ;  c,  the  meibomian  glands,  which 
secrete  the  oily  fluid. 

19* 


2^2 


PHYSIOLOGY. 


51.  There  is  a  striking  proof  of  design  in  the  manner  in 
which  the  opaque,  lining  membrane  of  the  eye-lids  becomes 
transparent,  as  it  is  reflected  over  the  cornea.  But  we  can 
illustrate  this  more  clearly  by  means  of  the  following  dia- 

gram. 

Fig.  24. 


The  eye-lids  viewed  from  before ;  a,  a,  the  lachrymal  canals ;  h,  the 
iarchrymal  sack.  The  lachrymal  sack  is  a  bag  of  an  oval  shape,  fixed 
to  the  end  of  the  double  canal,  and  lies  in  a  depression  of  the  nasal 
bones.  It  terminates  in  a  tube  called  the  duct,  which  passes  through 
a  hole  made  for  it,  in  the  bones  of  the  nose,  and  opens  into  the  nos- 
tril. 

52.  It  is  now  well  ascertained  that  a  belief  in  superna- 
tural appearances,  and  stories  in  relation  to  seeing  ghosts, 
hobgoblins,  and  spectres,  have  arisen  from  optical  illusion. 
We  have  seen  how  a  person  in  delirium  tremens,  imagines 
that  he  sees  a  thousand  unreal  objects,  and  hears  a  thousand 
strange  voices  ;  the  same  phenomenon,  though  less  in  degree, 
may  happen  to  a  person  in  health,  owing  to  an  excitement 
in  some  portion  of  the  brain.,  I  have  heard  an  aged  rela- 
tive,  who  believed  in  witchcraft,  tell  of  frequently  having 
seen  the  ghost  of  some  deceased  friend,  and  once  of  having 
fired  at  a  deer  three  times,  in  the  twilight,  while  he  was 
cropping  the  tender  grain  just   springing  out  of  a  newly- 


SENSE    OF    SIGHT.  223" 

sown  field,  without  frightening  the  animal ;  and  when  at 
length  he  suddenly  disappeared,  no  tracks  or  traces  of  him 
could  be  discovered  on  the  soft  mould.  Nothing  could  con- 
vince the  old  gentleman  that  his  sight  had  deceived  him, 
that  these  objects  had  only  existed  in  his  brain. 

53.  One  source  of  deception  lies  in  the  fact  that,  indirect 
a&  well  as  direct  vision  is  intermittent,  as  any  one  may 
learn  by  attempting  to  read  small  print  by  moonshine,  or  in 
twilight,  or  by  looking  at  a  single  star  for  some  time,  when 
it  will  be  found  to  vanish  often  and  reappear.  In  an  ob- 
scure light  we  find  that  a  painful  efibrt  is  required  to  distin- 
guish objects ;  and  after  all  they  appear  and  disappear,  be- 
cause the  impression  they  make  upon  the  retina  is  not 
sufficiently  vivid  to  be  continuous.  We  can  easily  imagine 
therefore,  that  in  the  dusk,  to  a  person  who  is  ignorant  of 
this  fact,  the  sudden  disappearance  and  reappearance  of 
objects  must  seem  very  extraordinary 

54.  Dr.  Paley  remarks  that,  "  were  there  no  example  in 
the  world  of  contrivance  except  that  of  the  eye,  it  would  be, 
alone,  sufficient  to  support  the  conclusions  which  we  draw 
from  it,  as  to  the  necessity  of  an  intelligent  Creator."  When 
we  look  at  a  telescope,  and  see  how  it  consists  of  a  tube 
composed  of  various  pieces,  containing  several  glasses  or 
lenses  placed  at  diflTerent  distances  in  order  to  refract  the 
rays  of  light,  and  bring  them  to  a  focus  ;  how,  within  it, 
there  is  a  partition  of  metal,  through  which  is  a  round  hole 
in  the  centre  for  the  purpose  of  lessening  the  surface  of  the 
lens  on  which  the  rays  of  light  strike  ;  and  when,  in  addi- 
tion to  all  this,  we  see  the  inside  painted  black,  to  absorb  the 
oblique  and  scattering  rays  that  would  otherwise  render 
objects  confused  and  indistinct ;  when  we  see  all  these 
things,  we  immediately  say,  here  are  marks  of  design,  here 
is  evidence  of  wise  and  skilful  contrivance  !  and  yet  the 
telescope  is  but  a  close  imitation  of  the  human  eye,  which 
had  God  for  its  designer.  When,  also,  we  look  at  the  ca- 
mera obscura  and  see  a  tight,  dark  box,  with  a  lens  fitted  in^ 


224  PHYSIOLOGY. 

to  it,  through  which  the  light,  passing,  falls  upon  a  screen 
behind,  forming  an  inverted  image  of  the  object  represented, 
we  say  at  once  here  is  design  !  But  this  instrument  also  is 
copied  from  the  human  eyel  -      . 


Questions. — ^What  is  said  of  the  sense  of  sight  ?  What  are  the  coats 
of  the  eye  ?  Describe  the  scelerotic  ? — the  choroid  ?  What  is  the  pig- 
raentum  nigrum  ?  Is  it  ever  absent  ?  Describe  the  retina  ?  Illustrate  the 
minuteness  with  which  objects  are  painted  on  it  ?  Describe  the  cornea  ? 
— the  ciliary  ligament  ?  What  is  said  of  these  tunics  in  the  lower 
order  of  animals  ?  What  is  the  iris  ?  How  does  it  contract  and  di- 
late 1  Are  the  muscles  ever  under  the  control  of  the  will  ?  What  is 
said  of  the  iris  among  the  lower  animals  ?  Describe  the  ciliary  pro. 
cesses  ?  What  are  the  humours  of  the  eye  ?  Describe  the  aqueous  ? 
the  crystalline  ? — the  vitreous  ?  Explain  some  of  the  laws  of  vision  ? 
What  is  a  lens  ?  How  many,  and  what  kinds  of  lenses  are  there  T 
What  effect  on  light  has  a  concave  ?  a  convex  ?  a  plain  lens  ?  Illus- 
trate this  by  the  humours  of  the  eye.  Are  images  erect  on  the  retina? 
Where  do  the  rays  cross  ?  How  do  you  explain  why  we  do  not  see 
objects  inverted  ?  Why  do  we  not  see  objects  double  ?  Why  do  riv- 
ers appear  shallower  than  they  are  ?  To  what  is  short-sightedness 
owing  ?  How  may  it  be  corrected  ?  What  is  long-sightedness  ?  What 
is  the  remedy  ?  Are  there  persons  who  cannot  distinguish  colours  ? 
To  what  is  this  owing  t  What  is  said  of  compound  eyes  ?  How 
many  muscles  are  there  to  move  the  eye  ?  Describe  them  ;  the  recti ; 
the  oblique.  What  are  the  defences  of  the  eye  ?  Describe  the  orbit ; 
the  eyelids ;  the  muscles  of  the  lids.  Are  they  voluntary  muscles  ? 
How  are  objects  carried  into  the  angle  of  the  eye  ?  What  is  the  use 
of  eyelashes? — of  eyebrows?  How  are  the  tears  secreted?  How 
carried  out  of  the  eye  ?  What  has  led  to  a  belief  in  supernatural  ap^ 
pearances  ? 


CHAPTER  XVir. 


THE    SENSE    OF    HEARING. 


1.  Through  the  sense  of  hearing,  we  obtain  a  know- 
ledge of  the  peculiar  vibrations  of  sonorous  bodies,  which 
constitute  sounds.  The  organ  of  hearing  is  very  complica- 
cated,  like  that  of  sight,  and  the  precise  office  of  the  differ- 
ent parts  is  not  yet  fully  known  ;  it  is,  however  generally 
divided  into  the  outer,  the  middle,  and  the  inner  part,  and 
the  auditory  nerve. 

2.  The  External  Ear. — The  outer  'part  (?f  the  organ  of 
hearing  consists  of  what  is  called  the  external  ear,  and  the 
cavity  which  leads  to  the  ear-drum  ;  and  is  composed  chiefly 
of  cartilage,  covered  with  the  skin,  and  supplied  with  blood- 
vessels and  nerves.  Its  use  is  to  collect  sound,  or  rather  the 
vibrations  of  the  air,  and  transmit  them  through  the  tube 
that  leads  to  the  ear-drum.  For  this  purpose  it  is  admirably 
contrived  ;  its  surface  being  smooth  and  folded  into  grooves, 
which,  assisted  by  a  raised  border  and  several  concave 
spaces,  conduct  whatever  sounds  fall  upon  it,  with  the  great- 
est certainty,  directly  to  the  drum  of  the  ear.  The  external 
ear  is  furnished  with  muscles,  and  savages  are  said  to  have 
the  power  of  raising  or  bringing  forwards  their  ears,  like  a 
horse,  to  catch  sounds  as  they  come  from  different  direc- 
tions ;  but  the  habits  of  civilized  life  destroy  this  faculty. 
The  following  cut  represents  the  external  ear,  and  the  mus- 
cles by  which  it  is  moved,     (See  Fig.  1.) 

3.  Various  names  are  assigned  to  the  different  portions 
of  the  external  ear,  such  as  helix  to  the  outer  border,  scapha, 
the  large  boat-like  depression,  &;c.  ;  but  passing  these  by,  as 
of  little  importance,  we  remark  that  the  external  ear  is  con- 
fined to  the  class  mammalia,  nor  does  it  always  exist  among 
them,  for  the  mole,  the  water-shrew,  and  other  diving  animals, 


226 


PHYSIOLOGY, 
Fig.   1. 


External  Ear  and  Muscles. 

seals  and  whales,  are  destitute  of  it.  Indeed,  as  water  is  a 
much  better  conductor  of  sound  than  air,  there  would  seem 
to  be  little  occasion  for  the  external  ear  in  them  ;  but  they 
suffer  in  consequence,  when  they  attempt  to  live  with  their 
heads «ut  of  water.  Owing  to  this  obtuseness  of  hearing 
in  the  whale,  he  is  easily  approached  by  the  whaler,  and  be- 
fore he  hears  the  oars  of  his  enemy,  the  harpoon  is  fixed 
into  his  unwieldy  carcass.  In  like  manner,  the  walrus  and 
the  seal  remain  unconscious  of  the  footsteps  of  their  foe,  till 
it  is  too  late  to  retreat.  In  land  animals  that  are  timid,  as 
the  hare  and  rabbit,  the  ear  is  very  large^  so  that  they  may 
be  apprized  of  the  approach  of  their  enemy  in  time  to  flee 
to  a  place  of  safety. 

4.  The  Tube  of  the  External  Ear. — This  is  the  passage, 
called  by  anatomists  meatus  auditorius  externus,  which  ex- 
tends from  the  outer  ear  to  the  tympanum  or  drum,  which  i& 
stretched  across  its  inner  end.  This  passage  is  about  ten 
lines,  or  nearly  an  inch  in  length  ;  and  pursues  a  somewhat 
winding  course  inwards,  a  little  forwards  and  downwards  ; 
its  external  portion  being  composed  of  cartilage,  and  its  in- 
ternal of  bone.  The  width,  as  well  as  tension  of  this  tube, 
are  effected  by  the  motions  of  the  jaw,  as  any  one  can  learn 


THE    SENSE    OF    HEARING. 


227 


by  placing  his  little  finger  in  his  ear,  and  then  opening  and 
closing  the  mouth.  This  is,  no  doubt,  one  reason  why  a 
person  stands  with  his  mouth  open  when  he  is  listening  at- 
tentively.  This  tube  being  constantly  open,  is  liable  to  the 
entrance  of  foreign  bodies,  such  as  dust,  insects,  and  the 
like.  But,  like  the  eye,  it  is  not  left  without  means  of  de- 
fence, for  on  its  inside,  there  are  numerous  fine  bristles, 
which  interlace  and  prevent  the  entrance  of  any  thing  but 
sound  ;  while  between  the  roots  of  these  hairs,  there  are 
numerous  little  glands,  which  secrete  a  nauseous  bitter  wax, 
which  by  its  offensiveness,  either  deters  insects  from  enter- 
ing, or  if  they  do,  entangles  them,  and  thus  prevents  any 
further  advance.  This  wax  often  becomes  hard,  and  ob- 
structs the  tube,  causing  more  or  less  deafness.  This  form 
of  deafness  is  easily  cured,  although  it  may  have  existed 
even  for  years.  When  the  ear  is  dry,  from  a  deficiency  oii 
wax,  the  hearing  also  becomes  imperfect,  as  also  whea  it  is 
thin  and  purulent. 

Fig.  2. 


General  sectional  view  of  the  structure  of  the  ear ;  a,  the  meatus 


228  PHYSIOLOGY. 

auditorius  externus  ;  b,  the  tympanum  ;  c,  the  malleus  ;  d,  the  incus  ; 
e,  the  OS  orbiculare ;  /,  the  stapes  ;  g,  the  semicircular  canals  ;  h,  the 
cochlea  ;  i,  the  meatus  auditorius  internus ;  kf  the  eustachian  tube. 

5.  Membrane  of  the  Drum,  stretched  across  the  inner  end 
of  the  auditory  tube,  is  a  membrane,  called  by  anatomists  the 
membrane  of  the  tympanum,  {membrana  tympani,^  or  drum  of 
the  ear.  It  is  somewhat  oval  in  shape,  but  hollowed  out,  or 
depressed  at  the  centre,  where,  as  we  shall  presently  see,  it 
is  fastened  to  the  end  of  a  small  bone.  This  membrane  is 
tense  like  a  drum-head,  thin,  and  transparent.  Its  use  is  to 
convey  the  vibrations  of  the  atmosphere  to  the  expansion  of 
the  optic  nerve  in  the  internal  ear.  It  does  not  seem  entire- 
ly essential  to  the  function  of  hearing,  as  the  hearing  some- 
times remains  after  it  is  destroyed.  When  it  is  ruptured,  a 
person  can  force  the  air  out  of  his  ear  ;  but  while  it  remains 
entire,  it  is  impossible  for  insects  or  other  bodies  to  get  into 
the  dinim,  as  is  generally  believed.  The  drum  is  capable  of 
being  rendered  more  or  less  tense,  and  thus  of  moderating 
the  intensity  of  vibrations  transmitted  to  it. 

6.  The  Drum. — What  is  called  the  drum,  or  tympanum, 
is  an  irregular  cylindrical  cavity,  separated  from  the  external 
passage  by  the  membrane  of  the  drum.  It  contains  the  little 
bones  of  the  ear,  the  openings  to  the  labyrinth  an^  other 
parts  of  the  organ.  Anteriorly  a  passage  leads  from  this 
cavity,  forwards  and  downwards  to  the  throat,  called  the 
Eustachian  tube.  .  Posteriorly  there  are  several  openings  into 
osseous  cells,  called  the  mastoid  cells,  which  are  situated  in 
that  projecting  process  of  bone  immediately  back  of  the  ear. 
This  cavity  then  is  filled  with  air. 

7  Eustachian  Tube. — I  have  stated  that  this  tube  leads  from 
the  drum  into  the  mouth,  and  serves  for  the  introduction  of 
air  into  the  internal  ear.  The  necessity  of  such  a  contri- 
vance is  obvious  from  the  fact,  that  sounds  cannot  be  trans- 
mitted through  a  vacuum,  as  is  shown  in  the  common  ex- 
periment of  ringing  a  hell  in  an  exhausted  receiver,  when 
no  sound  is  made.      So  in  a  drum,  there  is  an  air-hole^  else 


THE    SENSE    OF    HEARING. 


229 


the  sound  would  be  flat,  and  the  head  liable  to  be  ruptured. 
When  this  tube  is  obstructed  by  the  swelling  of  its  lining 
membrane  from  cold,  or  the  accumulation  of  secretion  in  the 
passage,  deafness  is  the  consequence.  This  passage  is  about 
an  inch  and  a  half  in  length,  and  widens  from  the  ear  te  the 
throat  like  a  trumpet.  When  deafness  occurs  from  com- 
plete closure  of  this  tube,  hearing  may  be  restored  by  per- 
forating the  membrane  of  the  drum.  We  may  ascertain 
with  a  good  degree  of  certainty  whether  deafness  arises  from 
this  cause,  by  placing  a  watch  between  the  teeth,  if  its  mo- 
tions are  audible,  we  may  conclude  that  the  essential  organ 
of  hearing  is  unaffected. 

8.  Bones  of  the  Ear. — These  are  four  in  number,  and  are 
so  connected  with  each  other  in  the  drum,  that  they  serve 
to  transmit  vibrations  of  the  membrane  of  the  tympanum  to 
the  internal  ear.  From  their  shape,  they  are  called  the 
mallet,  the  anml,  the  orbicular,  and  the  stirrup  bones,  and  are 
exhibited  in  nearly  the  natural  size  in  the  following  cut. 

Mallens,  Incus,  and  Orbiculare,  Stapes, 
Fig.  3. 


Bones  of  the  ear. 

These  bones  are  very  hard  and  brittle,  have  no  cartilage  on 
their  articular  surfaces  like  other  bones  ;  neither  are  they 
furnished  with  ligaments  or  synovia,  but  their  dry  and 
polished  surfaces  are  accurately  fitted  to  each  other  in  the 
form  of  a  bent  lever  ;  and  in  this  way,  being  connected  and 
held  together  by  the  little  muscles,  by  which  they  are  moved 
and  attached  to  each  other,  the  intensity  of  vibration  which 
they  receive  from  the  membrane  of  the  drum  is  not  blunted. 

20 


230  PHYSIOLOGY. 

The  handle  of  the  mallet  is  attached  to  the  membrane  of  the 
drum^  and  its  other  extremity  rests  on  the  anvil,  which  is 
connected  with  the  orbicular  bone,  the  smallest  in  the  body, 
and  not  much  larger  than  a  grain  of  sand.  This  is  inter- 
posed between  the  round  bone  and  the  stapes,  whose  base 
rests  upon  the  membrane  of  the  oval  fenestra.  Now  the 
contraction  of  the  muscles  which  connect  these  bones,  puts 
the  drum-head  on  the  stretch,  and  thus  adapts  it  for  the  ready 
transmission  of  sound. 

9.  Mastoid  Cells. — These  are  seated  in  the  hard  portion 
of  the  temporal  bone,  and  are  also  filled  with  air.  The  ear 
m  thus  surrounded  with  an  atmosphere  of  its  own.  In  the 
elephant,-  the  two  tables  of  the  skull  are  separated  from  each 
other  by  a  bony  cellular  structure  to  the  extent  of  upwards 
of  a  foot,  and  these  cells  are  filled  with  air  which  communi- 
cate with  the  drum  of  the  ear.  We  find  in  the  cat  tribe,  in 
dogs,  and  in  gnawing  animals,  that  there  is  a  hollow  sphere 
of  veiy  hard  bone  attached  to  the  drum,  shaped  something 
like  a  conch,  and  well  adapted  for  reflecting  the  vibrations 
of  sound,  and  rendering  them  more  intense,  like  the  sound- 
ing board  of  a  piano-forte.  A  similar  hard  conch  is  found 
in  the  whale  tribe.  The  two  tables  of  the  skull  in  birds  are 
also  widely  separated,  thus  rendering  them  lighter,  and  as 
the  cells  communicate  with  the  drum,  doubtless  for  the  pur- 
pose of  increasing  the  volume  of  air  for  the  reception  of 
Tib  ration.  » 

10.  Petrous  Portion. — The  internal  ear  is  situated  in  a 
portion  of  the  temporal  bone,  called  petrous,  from  petra,  a 
rock,  because  of  its  solid  structure.  The  object  of  this  is 
evident  from  the  fact,  that  hard  elastic  substances  transmit 
vibrations  of  sound  far  better  than  matter  of  a  softer  texture. 
This  portion  of  the  temporal  possesses  indeed  almost  an 
ivory  hardness,  being  the  densest  structure  in  the  animal 
body,  next  to  the  enamel  of  the  teeth  ;  and  in  this  solid  body 
the  labyrinth  of  the  ear  is  situated.  Now  in  whales,  the 
skeleton  is  formed  of  loose  spongy  bones,  with  a  considerable 


THE    SENSE    OF    HEARING.  231 

quantity  of  oil,  collected  in  their  cells.     To  compensate  for 

this  soft  structure,  whales  are  furnished  with   a  sounding 

board,  or  the  dense  conch,  above  mentioned.     In  fishes,  we 

often  find  several  of  these  little  bony  concretions,  of  a  smooth 

and  polished  appearance,  and  hard  and  brittle  as  porcelain. 

These  are  often  seen  in  cutting  up  boiled  fish,  when  placed 

upon  the  table,  but  few  are  aware  of  the  uses  they  serve  in 

perfecting  the  organ  of  hearing. 

11.  In  order,  however,  to  understand  the  precise  function 

of  these  bones,  it  will  be  necessary  to  examine  a  little  more 

into  their  situation  and  connection.     In  the  following  plan, 

they  are  represented,  greatly  magnified,  but  ea<;h  bone  in  its 

natural  position. 

Fig.  4. 


A,  the  malleus,  or  mallet,  with  its  long  handle  running  down,  to 
touch  with  its  delicate  extremity  the  membrane  of  the  drum.  B,  is  the 
incus,  or  anvil,  nicely  fitted  to  the  mallet,  and  showing  C,  the  orbicular 
bone  placed  between  its  termination,  and  D,  the  stirrup.  The  line  a,  &, 
represents  the  centre  of  motion  of  the  malleus,  and  c,  d,  the  centre  of 
motion  of  the  incus.  Now  this  chain  of  bones  acts  on  the  principle  of 
a  long  lever,  as  a  small  motion  at  one  end  of  a  long  pole  serve  to  move 
it  through  a  wide  space  at  the  other.  As  Sir  Charles  Bell  explains  it, 
the  head  of  the  malleus  is  so  articulated  with  the  body  of  the  incus, 
that  the  centre  of  motion  of  the  incus  is  a  line  drawn  through  the  centre 
of  its  body,  and  consequently  thp  extremity  of  the  long  process,  to 


232  PHYSIOLOGY. 

which  the  orbicular  and  stirrup  bones  are  attached,  moves  through  a 
greater  space  than  that  which  receives  the  impulse  of  the  head  of  the 
malleus.  Thus  a  very  small  degree  of  motion,  communicated  by  the 
head  of  the  malleus  to  the  body  of  the  incus,  is  greatly  increased  in 
the  extremity  of  the  long  process  of  the  incus  ;  and  consequently  this 
mechanism  assists  greatly  in  giving  strength  to  the  vibrations  trans- 
mitted to  the  internal  ear. 

12.  Now  in  distinguishing  low  soirads,  the  drum  head  rs 
supposed  to  be  put  upon  the  stretch,  chiefly  by  the  aid  of  one 
little  muscle,  called  tensor  tympanic  which  is  attached  to  the 
malleus,  and  the  centre  of  the  membrane,  so  that  when  it 
acts,  it  pulls  the  long  handle  of  that  bone,  and  draws  the  tym- 
panum inwards.  Thus  being  made  tense,  it  is  prepared  for 
the  reception  of  low  sounds.  When  sounds  are  so  acute  as 
to  be  painful,  and  we  wish  to  diminish  their  intensity,  this 
muscle  relaxes,  and  the  tympanum  becoming  comparatively 
flaccid,  a  deadened  muffled  impression  is  transmitted  to  the 
brain,  precisely  as  when  we  muffle  a  drum.  This  relaxation 
is  also  aided  by  a  muscle  expressly  prepared  for  that  pur- 
pose, called  laxator  tyinpani,  which  arises  from  the  temporal 
bone  and  is  inserted  into  the  handle  of  the  malleus,  so  as  to 
pull  it  forwards. 

13.  We  traced  the  progress  of  sound  through  the  external 
ear,  the  auditory  passage,  and  the  chain  of  bones,  to  the 
stapes.  Now,  if  the  reader  will  look  at  plate  II.,  he  will  see 
that  the  base  of  the  stirrup-bone  is  smooth  and  flat  ; 
this  is  placed  directly  upon  the  passage  into  the  labyrinth, 
Cd\\e^  foramen  ovale,  as  a  seal  is  placed  on  an  impression,  or 
a  valve  upon  a  hole.  The  cavities  we  have  described  are 
filled  with  air,  those  now  to  be  mentioned  are  filled  with  wa- 
ter. The  labyrinth  then,  which  has  been  called  the  audience 
chamber  of  the  ear,  consists  of  three  parts,  viz.,  the  vesti- 
bule or  lobby,  which  m*ay  be  compared  to  the  porch  of  a 
building ;  three  semi-circular  canals  shaped  like  three  hoops, 
tied  together  at  one  point,  and  their  opposite  points  widely 
separated ;  and  lastly,,  the  cochleay  which  closely  resembles 


THE    SENSE    OF    HEARING. 


233 


a  snail  shell,  consisting  of  two  spiral  canals,  which  wind 
round  a  central  pillar  twice  and  a  half,  and  also  separated 
by  a  spiral  partition. 

Fig.   9. 


Section  of  the  Cochlea. 

14.  The  stapes  then  rests  upon  the  membrane  which  is 
placed  across  the  opening  into  the  labyrinth.  When  the 
tympanum,  or  drum-head,  is  impressed  by  the  vibrations  of 
the  air,  the  vibration  is  communicated  to  the  little  bones, 
and  through  them  to  the  membrane  of  the  labyrinth,  which 
causes  corresponding  tremors  in  the  fluid  which  fills  its 
winding  canals,  and  the  spiral  passages  of  the  cochlea  ; 
upon  which  the  auditory  nerve  is  spread  out  like  a  fine 
pulpy  web,  in  the  same  manner  as  the  retina  is  spread  out 
upon  the  choroid  coat  of  the  eye,  or  the  olfactory  nerve 
upon  the  mucous  membrane  of  the  nose,  and  thus  is  sound 
conveyed  by  the  nerve  to  the  brain. 

15.  The  object  of  these  spiral  passages  returning  into 
themselves  is,  doubtless,  to  furnish  an  extensive  surface, 
within  a  small  space,  for  the  expansion  of  the  auditory 
nerve,  and  also  that  the  undulations  of  the  fluid  which  fills 
them  after  passing  from  the  oval  fenestra  along  the  winding 

20* 


234  PHYSIOLOGY. 

passages,  and  up  the  spiral  staircase  of  the  cochlea,  might 
come  down  to  the  round  fenestra,  whose  elastic  membrane 
would  transmit  the  vibration  in  the  opposite  direction. — 
When  the  sounds,  therefore,  have  done  their  office,  in  order 
that  the  hearing  might  not  be  rendered  confused  by  a  pro- 
longed vibration  of  the  fluid,  as  an  echo  is  repeated  between 
two  mountains,  as  they  strike  the  above  named  membrane, 
they  are  given  off  ta  the  air  in  the  tympanum,  and  there  the 
vibrations  end ;  for  we  have  seen  that  it  is  probably  the 
bones  in  the  tympanum  chiefly,  and  not  the  air,  which  trans- 
mits impressions  to  the  fluids  of  the  labyrinth,  and  that  they 
receive  their  impulse  from  the  drum  of  the  ear. 

16.  Sound. — Sound  has  no  distinct  existence,  but  is  the 
result  of  certain  conditions  of  bodies.  We  see  how,  by 
throwing  a  pebble  into  a  lake  of  water  at  rest,  the  undula- 
tions spread  in  every  direction,  in  the  foi'm  of  a  circle,  until 
the  impulse  is  lost  in  the  distance.  So  in  air,  frequent  vi- 
brations produce  sound  ;  and  hearing  has  been  defined  to  be 
that  function  by  which  we  obtain  a  knowledge  of  the  vibra- 
tory motions  of  bodies.  These  motions  produce  waves  or 
undulations  in  the  air,  which  are  propagated  in  every  direc- 
tion, as  the  circular  waves  are  produced  in  the  lake,  by 
throwing  in  the  pebble. 

17.  Air  is  the  common  vehicle  of  sound,  though  all  elastic 
bodies  are  capable  of  conveying  it.  Water  conveys  sound 
better  than  air,  and  some  solid  bodies  better  than  either.  If 
two  stones  are  struck  together  under  water,  a  person  whose 
head  is  under  the  surface  may  hear  the  sound  at  a  great  dis- 
tance. A  blow  struck  with  a  hammer  by  a  workman  in  a 
diving  bell,  far  below  the  surface  of  the  water,  is  heard  dis- 
tinctly many  fathoms  above.  So  also  if  the  ear  be  applied 
to  the  end  of  a  lono;  stick  of  timber  a  slight  scratch  made  at 
the  other  extremity  will  be  distinctly  heard.  The  report  of 
a  cannon  is  heard  to  a  much  greater  distance  over  the  frozen 
surface  of  snow  ;  and,  under  such  circumstances,  firing  has 
been  heard  from  one  to  two  hundred    miles.     Savages  are 


THE    SITNSE    OF   HEARING.  235 

acquainted  with  this  fact,  for  they  apply  their  ears  to  the 
ground  to  hear  the  approaching  footsteps  of  their  enemy  or 
their  prey.  An  easy  way  to  tell  whether  a  tea-kettle  boils, 
is  to  touch  it  with  a  stick,  and  place  the  other  end  to  the 
ear.  On  this  principle,  I  suppose,  watchmen  strike  the  curb 
stone  with  their  clubs,  as  the  sound  is  communicated  much 
farther  than  it  was  formerly  by  means  of  their  rattle.  So 
also  a  musical  box,  when  held  in  the  hand  is  scarcely  heard, 
but  when  placed  on  a  bureau  or  sounding  board,  it  "dis- 
courseth  most  eloquent  miisic."  The  stethoscope  now  used 
by  physicians  to  assist  in  determining  the  nature  of  many 
diseases  is  derived  from  a  knowledge  of  this  principle.  It  is 
merely  a  cylinder  of  woody  about  an  inch  in  diameter,  one 
end  of  which  is  placed  on  the  surface  of  the  body  over  the 
diseased  part,  and  the  other  applied  to  the  ear ;  sound  is  thus 
carried  along  the  tube,  and  most  important  aid  is  derived  to 
the  skilful  physician,  in  ascertaining  the  nature  and  seat  of 
all  diseases  of  the  heart  and  lungs. 

18.  The  transmission  of  sound  is  affected  materially  by 
the  condition  of  the  atmosphere,  with  respect  to  tempera- 
ture, moisture,  &c.  During  the  night,  when  the  air  is  still, 
and  of  uniform  density  and  temperature,  sounds  are  heard 
to  a  great  distance  ;  but  when  it  is  loaded  with  vapors,  as  in 
a  fall  of  snow  or  rain,  sounds  are  more  limited,  and  rendered 
confused  and  indistinct. 

19.  The  density  of  the  air  has  a  great  effect  upon  the 
ti'ansmission  of  sound.  In  a  dry,  cold  atmosphere,  at  the 
level  of  the  sea,  sounds  are  transmitted  to  vast  distances, 
w^iile  on  high  mountains,  such  as  the  Andes,  or  even  Mont 
Blanc,  the  report  of  a  pistol  is  not  louder  than  that  of  an 
Indian  cracker.  The  wind,  also,  has  a  great  influence  in 
aidino;  or  retarding  the  transmission  of  sound.  Sound  is 
also  reflected  like  light,  and  indeed  is  subject  to  the  same 
laws,  for  the  angle  of  reflection  is  always  equal  to  the  angle 
of  incidence.  Reflected  sound  is  termed  an  echo.  The 
rolling  of  thunder  is  supposed  to  depend  partly  on  the  sound 


236  PHYSIOLOGY. 

being  reflected  from  cloud  to  cloud,  and  through  strata  of 
air  of  different  densities,  though  it  also  arises  from  a  dis- 
charge  of  electricity,  through  a  wide  extent  of  air.  In  this 
case,  as  the  sound  from  the  point  nearest  the  hearer  reaches 
his  ear  first,  and  some  moments  elapse  before  that  from  the 
more  distant  arrives,  there  must  consequently  be  a  continued 
peal.  Some  of  our  large  public  houses  and  manufactories 
are  fitted  with  pipes  for  conveying  intelligence  to  distant 
apartments,  attention  being  attracted  by  ringing  a  bell. 

20.  It  has  been  doubted  whether  sound  can  be  propagated 
from  one  medium  to  another,  as  from  air  to  water.  It  is 
now  known,  however,  that  if  a  musket  is  discharged  over  a 
person  who  is  under  water,  he  will  hear  the  report.  The 
question  has  also  arisen,  whether  sound  can  be  propagated 
from  water  to  the  air  again.  This  is  easily  proved  by  strik- 
ing two  stones  together  under  water,  although  we  are  told 
that  persons  in  a  diving-bell  under  water,  could  not  hear  a 
musket  discharged  immediately  over  it.  But  here  the  sound 
had  to  be  communicated  from  the  air  to  the  water,  and  from 
the  water  to  the  air  again.  Sound  travels  at  the  rate  of 
eleven  hundred  and  forty-two  feet  in  a  second,  or  a  mile  in 
four  seconds.  As  hght  travels  much  faster,  we  see  the  flash 
of  a  gun  before  we  hear  the  report.  This  will  enable  us  to 
tell  in  a  thunder  storm  how  far  we  are  from  a  thunder-cloud  ; 
as  we  have  only  to  allow  eleven  hundred  feet  for  each  se- 
cond, between  the  time  when  the  flash  is  seen  and  the  report 
heard,  and  one  beat  of  the  pulse  for  a  second.  In  this  way, 
too,  the  distance  of  a  ship  of  war  at  sea  is  often  ascertained 
by  those  on  board  of  the  vessel  she  is  in  pursuit  of.  Solids 
and  fluids  convey  sound  not  only  more  perfectly,  but  also 
more  rapidly  than  air.  It  is  found  that  the  velocity  of 
sound  in  water,  is  about  four  thousand  nine  hundred  feet  in 
a  second,  being  between  four  and  five  times  more  rapid  than 
it  is  through  air.  Sound  passes  through  tin  at  the  rate  of 
eight  thousand  one  hundred  and  seventy-five  feetf  and  through 
iron,  glass  and  wood,  eighteen  thousand  five  hundred  and 


THE    SENSE    OF    HEARING.  237 

thirty  feet  in  a  second.  This  explains  why,  when  a  gun  is 
fired  at  a  distance  over  the  surface  of  a  frozen  lake,  we  hear 
two  reports  after  we  see  the  flash  ;  first  a  sharp  and  loud 
one,  transmitted  by  the  solid  ice,  and  then  a  weaker  and 
duller  one,  through  the  air.  Franklin,  however,  found  by 
his  experiments,  that,  after  travelling  about  a  mile  through 
the  water,  sound  lost  some  of  its  intensity,  which  indeed 
might  be  expected.  Musical  tones  are  said  to  be  acute  when 
the  intervals  between  the  vibrations  are  short,  and  grave 
when  they  are  long.  Thus  a  flute  called  an  octave  produces 
a  shriller  sound  than  the  common  flute  ;  a  fiddle  than  a  bass 
viol.  The  strings,  too,  of  a  violin,  which  are  designed  for 
high  or  acute  notes,  are  smaller  than  the  others,  that  their 
vibrations  may  be  more  rapid ;  while  those  which  make  the 
grave  tones  are  large,  and  wound  round  sometimes  with  fine 
wire,  to  increase  the  weight,  and  make  them  vibrate  more 
slowly.  It  is  the  quality  and  variety  of  the  sounds  which, 
in  musical  tones,  gives  the  hearer  so  much  pleasure. 

21.  In  the  lower  order  of  animals,  hearing  is  performed 
by  means  of  an  apparatus,  much  more  simple  than  in  man. 
Some  of  them  have  merely  a  membranous  sac,  supplied  with 
nervous  threads.  This  is  even  the  case  in  fishes,  which  re- 
quire neither  tympanum  nor  hones,  nor  any  of  the  accessory 
paTts  found  in  land  animals,  as  the  undulations  of  water  strike 
with  greater  force  upon  the  organ  of  hearing  than  those  of 
air.  The  apparatus  of  hearing  in  the  frog  is  very  singular, 
and  designed  so  as  to  enable  the  animal  to  hear  both  in  air 
and  water. 

22.  Animals  with  long  ears  are  able  to  move  them  by 
muscles  for  that  purpose,  and  turn  them  to  the  point  whence 
the  sound  proceeds.  This  may  be  seen  in  the  horse,  which 
turns  his  ear  always  in  the  direction  of  the  sound.  In  stage 
horses,  we  often  see  the  leaders  turn  their  ears  forward, 
while  those  behind  turn  theirs  backward.  Some  men  also 
have  the  power  of  moving  their  ears. 

23.  Like  all  our  ather  senses,  that  of  hearing  is  capable 


238  PHYSIOLOGY. 

of  much  improvement  by  cultivation.  The  Indian  in  the 
forest,  accustomed  to  listen  to  the  approach  of  his  enemies, 
or  of  his  prey,  acquires  such  acuteness  of  this  sense,  as  to 
hear  sounds  which  would  be  inaudible  to  those  who  live  amid 
the  din  of  civilized  life.  The  blind  also  excel  in  the  acute- 
ness of  hearing,  and  for  this  reason  especially,  acquire  great 
skill  in  performing  on  musical  instruments.  Shakspeare 
thus  describes  a  person  destitute  of  musical  taste. 

•'  The  man  that  hath  no  music  in  his  soul, 
Nor  is  not  moved  with  concord  of  sweet  sounds, 
Is  fit  for  treasons,  stratagems,  and  spoils  ; 
The  motions  of  his  spirit  are  dull  as  night. 
And  his  affections  dark  as  Erebus ; 
Let  no  such  man  be  trusted." 


Questions. — ^^"hat  are  sounds  ?  Describe  the  external  ear  ; — the 
tube  of  the  external  ear  ; — the  membrana  tympani ; — the  drum,  or  tym- 
panum ; — the  eustachian  tube.  How  many  little  bones  of  the  ear  are 
there  ?  Their  names  and  office  ?  How  are  low  sounds  perceived  ? 
What  is  the  use  of  the  spiral  passages  ?  How  is  sound  conveyed  ?  Is 
it  conveyed  by  solids  ; — by  water  ?  What  is  the  stethoscope  ?  Can 
sound  be  propagated  from  one  medium  to  another  ?  At  what  rate  does 
it  travel  ?  How  can  we  tell  the  distance  of  sound  ?  What  effect  has 
the  density  of  air  on  sound  ?  How  is  the  lengthened  peal  of  thunder 
explained  ?  How  is  hearing  performed  in  the  lower  order  of  animals? 
Can  hearing  be  improved  by  cultivation  ? 


CHAPTER  XVIII. 


RESPIRATION. 

1.  By  Respiration,  is  meant  the  process  of  taking  air  into 
the  lungs  and  throwing  it  out  again.  Inspiration  is  the  act 
of  drawing  the  air  in  ;  expiratio7i,  that  of  forcing  it  out. 
Respiration  is  essential  to  all  animal  existence.  It  is  in  the 
lungs  that  the  last  change  is  produced  in  the  assimilation  of 
the  food,  by  which  it  is  converted  into  that  vital  fluid,  which 
carries  life,  and  strength,  and  nourishment  to  every  fibre  in 
the  animal  system. 

2.  The  parts  concerned  in  respiration  may  be  arranged 
into  three  divisions,  viz.,  1,  the  hones  which  form  the  respir- 
atory  cavity ;  2,  the  muscles  by  which  these  bones  are  moved, 


Thorax,  or  chest ;  a,  the  sternum ;  h,  h,  the  spine ;  c,  c,  the  nbs. 


240  PHYSIOLOGY. 

and  the  size  of  the  cavity  regulated  ;  3,  the  respiratory  organs 
contained  within  the  cavity. 

3.  The  bones  which  enter  into  the  composition  of  the 
chest,  are  the  sternum,  or  breast-bone  ;  twelve  dorsal  vertehrae, 
and  twenty  four  ribs.  By  examining  the  preceding  plate, 
Fig,  1.,  the  sternum  will  be  seen  to  terminate  at  its  lower 
part  in  a  triangular  piece  of  cartilage,  which  lies  directly 
over  the  stomach,  and  may  be  felt  externally  ;  the  seven 
uppermost,  or  true  ribs,  will  be  seen  to  extend  the  whole 
distance  from  the  spine  to  the  sternum,  strips  of  elastic  car- 
tilage being  interposed  between  the  breast-bone  and  their 
anterior  extremities,  while  the  five  lower,  or  false  ribs,  are 
merely  attached  to  each  other  by  slips  of  cartilage  ;  the  two 
lower,  indeed,  float  loosely,  without  any  attachment  to  the 
others,  except  by  means  of  muscles. 

4.  I  have  already  stated  that  the  ribs  are  attached  to  the 
spine  at  an  acute  angle,  so  that  they  cannot  be  mo-ved  out 
of  their  ordinary  position,  without  enlarging  the  dimensions 
of  the  chest.  The  articulation  of  the  ribs,  both  at  the  spine 
and  sternum,  is  effected  by  means  of  cartilage,  thus  allowing 
sufficient  degree  of  motion  for  the  purposes  of  respiration  in 
a  healthy  state.  The  chest  expands  during  inspiration  for 
the  reception  of  air  ;  and  during  expiration,  it  contracts  to 
expel  air,  which  is  no  longer  useful.  There  are,  therefore, 
two  motions  required,  an  upward  and  an  outward ;  the  first 
increases  the  distance  between  the  spine  and  sternum  ;  the 
last,  that  between  the  ribs.  Now  these  motions  are  both 
effected  by  the  ribs,  and  they  are  so  articulated,  that  they 
cannot  perform  the  one  without  the  other.  By  looking  at 
the  cut,  then,  it  will  readily  be  seen  how  where  the  ribs  rise, 
the  sternum  will  be  pushed  out,  and  of  course  the  cavity  of 
the  chest  enlarged. 

5.  The  Muscles. — All  the  muscles  which  are  attached  to 
the  bones  just  described,  aid  more  or  less  in  respiration, 
though  the  intercostal  muscles  are  those  chiefly  concerned. 
These  run  from  one  rib  to  another,  filling  up  the  spaces,  be- 


RESPIRATION.  241 

tween  them.  These  muscles,  though  thin,  consist  of  a  double 
layer  of  fibres,  the  external  and  the  internal,  which  pass  in 
inverse  directions,  one  layer  from  above  downwards,  the  other 
from  behind  forwards,  from  edge  to  edge  of  the  ribs,  crossing 
each  other.  Now,  the  first  rib  being  fixed,  the  second  move- 
able, but  less  so  than  the  third,  the  third  less  than  the  fourth, 
and  so  on  through  the  whole  series ;  the  contraction  of  the 
intercostals  must  consequently  elevate  the  whole  series,  as 
the  upper  ribs  serve  as  fixed  points  for  the  action  of  the 
muscles. 

6.  The  chief  muscle,  however,  of  respiration,  is  the 
diaphragm.  By  the  aid  of  this,  the  capacity  of  the  chest  is 
enlarged  downwards,  as  we  have  seen  it  to  have  been  up- 
wards and  outwards  by  that  of  the  ribs.  The  diaphragm, 
or  midriff,  is  a  circular  muscle,  placed  transversely  across 
the  trunk,  nearly  at  its  centre,  dividing  the  cavity  of  the 
thorax  from  that  of  the  abdomen.  It  is  attached  to  the  in- 
side of  the  breast-bone  and  the  cartilages  of  the  false  ribs, 
and  is  fleshy  all  around  its  border,  but  tendinous  towards  its 
centre ;  the  surface  towards  the  abdomen  is  concave,  and 
that  towards  the  chest  convex.  Even  when  it  is  not  in 
action,  its  upper  surface  forms  an  arch,  the  convexity  of 
which  is  towards  the  thorax,  and  reaches  as  high  as  the 
fourth  rib.  The  central,  or  tendinous  portion  of  the  dia- 
phragm, is  attached  to  the  pericardium  supporting  the  heart ; 
and  is  nearly,  or  quite  immoveable,  in  order  to  afford  a  fixed 
point  for  the  action  of  the  muscular  fibres,  which  constitute 
its  sides.  Owing  to  this  arrangement,  its  motions  do  not 
interfere  with  those  of  the  heart. 

21  ^^^ -,^^ 


'-'■VlKtti: 


242 


PHYSIOLOGY. 
Fig.  2. 


View  of  the  diaphragm  ;  1,  cavity  of  the  thorax  ;  2,  diaphragm  sep. 
arating  the  cavity  of  the  thorax  from  that  of  the  abdomen  ;  3,  cavity 
of  the  pelvis. 

7.  During  the  act  of  inspiration,  the  diaphragm  contracts ; 
the  muscular  fibres  shorten  themselves,  and  the  muscle  de- 
scends, passing  from  the  fourth  rib  to  below  the  seventh, 
losing  the  arched  form,  as  represented  in  the  cut.  At  the 
same  time,  the  muscles  of  the  abdomen  are  protruded  for- 
wards, and  the  viscera  in  its  cavity  pushed  downwards. 
The  degree  in  which  the  capacity  of  the  chest  is  enlarged  by 
these  movements  is  very  satisfactorily  shown  in  the  follow- 
ing cut. 


RESPIRATION. 


243 


Fig,  3. 


Fig.  4. 


Fig.  Ill,  diaphragm  in  its  state  of  greatest  descent  in  inspiration  ; 
2,  muscles  of  the  abdomen,  showing  the  extent  of  their  protrusion  in 
the  action  of  inspiration.  Fig  IV,  diaphragm  in  the  state  of  its 
greatest  ascent  in  expiration ;  2,  muscles  of  the  abdomen  in  action 
forcing  the  viscera  and  diaphragm  upwards. 

8.  We  have  now  seen  how  the  capacity  of  the  chest  is 
enlarged  by  inspiration,  how  is  its  capacity  diminished  by 
expiration  ?  The  descent  of  the  ribs  is  occasioned  by  the 
elasticity  of  the  cartilages  and  ligaments  which  join  them 
to  the  sternum  and  the  spine.  Indeed  the  natural  condition 
of  the  chest  is  that  which  obtains  after  a  full  expiration ; 
and  therefore  we  may  consider  the  bones  which  form  the 
walls  of  the  chest,  and  the  muscles  which  cover  those  bones, 
as  anatagonizing  or  opposite  forces.  The  ribs,  then,  have  a 
natural  tendency  to  fall,  owing  to  their  peculiar  structure, 
as  well  as  their  position  ;  while  their  expansion  is  effected 
by  the  specific  action  of  their  muscles.  Besides  this,  when 
the  diaphragm  relaxes,  the  abdominal  muscles  contract  and 
push  the  abdominal  viscera,  and  the  diaphragm  also,  up  to- 


244  PHYSIOLOGY. 

wards  the  cavity  of  the  chest ;  and  thus  by  the  descent  of 
the  ribs  and  the  ascent  of  the  diaphragm,  the  capacity  of 
the  thorax  is  diminished,  and  the  motion  of  expiration  is 
completed. 

9.  The  third  division  of  our  subject  embraces  the  respir- 
atory organs,  or  the  lungs.  These  are  of  a  spongy  texture 
and  conical  shape,  and  fill  the  cavity  of  the  chest,  being 
composed  chiefly  of  blood-vessels,  and  air-vessels,  with  a 
small  portion  of  cellular  tissue.  They  are  called  liglits  in 
the  lower  animals.  There  are  two  lungs,  one  in  the  right, 
the  other  in  the  left  side  of  the  thorax  ;  and  each  of  these 
lungs  is  divided  into  several  lobes.  A  serous  membrane 
called  the  'pleura  surrounds  the  lungs,  and  is  reflected  upon 
the  walls  of  the  chest,  so  as  to  form  a  shut  sac,  into  which 
a  thin  watery  fluid  is  constantly  exhaled,  to  keep  the  sur- 
faces moist  and  slippery.  It  is  this  membrane  which  is  the 
seat  of  pleurisy..  There  are  two  pleurae,  each  of  which  is 
confined  to  its  own  side  of  the  chest,  lining  its  cavity,  and 
covering  the  lung.  Behind  the  breast-bone,  they  form  a 
partition,  called  mediastimim ;  between  the  sides  of  which, 
the  heart  and  pericardium  are  situated.  The  pleurae  serve 
to  attach  the  lungs  by  their  roots  to  their  respective  cavi- 
ties, and  to  facilitate  their  movements,  by  means  of  the  fluid 
exhaled  from  their  surfaces.  Each  lung  is  attached  to  the 
spine  by  its  roots,  where  blood-vessels,  nerves,  lymphatics, 
and  a  branch  of  the  windpipe  enter  it.     (See  Fig.  5.) 

10.  Thus  we  perceive  that  the  chest  is  divided  into  three 
compartments,,  one  on  each  side,  containing  a  lung  ;  the 
middle  one,  the  heart.  Between  these  there  is  no  communi- 
cation ;  so  that  if  a  fluid  is  thrown  into  one  of  them,  it  does 
not  find  its  way  into  the  others.  As  the  heart  lies  chiefly 
on  the  left  side,  the  lung  of  that  side  is  smaller  than  the  one 
on  the  right,  and  divided  into  only  two  lobes,  while  the  other 
is  divided  into  three.  The  lungs  are  the  lightest  texture  in 
the  human  body,  owing  to  the  air  which  they  contain,  and 
their  aspect  varies  with  the  age.     In  infancy  they  are  of  3 


RESPRIATION. 
Fig.  5. 


245 


a,  the  cut  edges  of  the  ribs,  forming  the  lateral  boundaries  of  ^e 
«avity  of  the  thorax ;  b,  the  diaphragm,  forming  the  inferior  boundary 
of  the  thorax,  and  the  division  between  the  thorax  and  the  abdomen  ; 
c,  the  cut  edges  of  the  abdominal  muscles,  turned  aside,  exposing  the 
general  cavity  of  the  abdomen. 

Fig.  1,  the  cut  edge  of  the  pericardium  turned  aside  ;  2,  the  heart ; 
3,  the  great  vessels  in  immediate  connexion  vi^ith  the  heart ;  4,  the 
trachea,  or  wind-pipe  ;  5,  the  lungs  ;  6,  the  liver ;  7,  the  stomach ; 
8,  the  large  intestine  ;  9,  the  small  intestines  ;  10,  the  urinary  bladder. 

pale  red,  in  youth  of  a  darker  colour,  and  in  old  age  of  a 
livid  blue. 

11.  The  air  enters  the  lungs  through  the  trachea  or  wind^ 

21* 


246 


PHYSIOLOGY. 


pipe.  This  is  a  tube,  made  up  of  little  rings,  cartilaginous 
in  front,  and  muscular  or  fibrous  behind ;  and  is  about  eight 
or  ten  inches  in  length.  It  lies  immediately  on  the  gullet  or 
(Bsophagus,  and  extends  from  the  larynx  to  the  third  vertebra 
of  the  back.  Hero  it  divides  into  two  branches,  called 
dronchia,  one  of  which  goes  to  the  right,  the  other  to  the 
left  lobe  of  the  lungs.  The  right  branch  divides  again  into 
&ree  principle  branches,  as  soon  as  it  enters  the  lung  ;  and 
the  left  into  two  ;  corresponding  to  the  number  of  lobes  in 
each  lung ;  then  they  subdivide  into  an  innumerable  number 
of  small  twigs,  like  the  branch  of  a  tree,  until  they  termi- 
nate in  those  small  cells  already  mentioned.  These  cells  are 
about  the  one  hundredth  of  an  inch  in  diameter, 

12.  The  bronchial  tube&  then,  terminate  in  minute  vesi- 
cles of  unequal  size,  which  are  of  a  cylindrical  and  some- 
what rounded  figure.  These  vesicles  are  large  enough  to  be 
visible  to  the  naked  eye,  and  present  something  of  the  ap- 
pearance of  a  cluster  of  currants  attached  to  their  stem,  as 
shown  in  the  following  cut : 

Fig.  6. 
View  of  the  Bronchial  Tubes,  terminating  in  Air  vesicles. 


External  view. — 1.  Bronchial  tube.  | 
2.  Air  vesicles.       I 


The  Bronchial  tube  and  Air 
vesicles  laid  open. 


It  should  be  borne  in  mind  that  the  ofiice  of  respiration  is 
to  bring  the  blood  in  contact  with  the  air,  and,  accordingly, 
the  lungs  are  so  constructed  as  to  allow  the  largest  possible 


RESPIRATION.  247 

quantity  of  deteriorated  blood,  to  enjoy  the  fullest  intercourse 
with  the  largest  possible  quantity  of  vital  air ;  and  all  the 
mechanism  of  bones  and  muscles  which  I  have  described, 
are  only  subservient  to  th  s  end.  Now  it  has  been  calcula- 
ted by  Hales,  that  each  air  cell  is  the  one  hundredth  part  of 
an  inch  in  diameter,  and  that  the  amount  of  surface  furnish- 
ed by  them,  collectively,  is  equal  to  twenty  thousand  square 
inches.  Other  physiologists  have  calculated  the  surface  to 
be  over  fifteen  hundred  cubic  feet,  and  Munroe  states  that  it 
is  thirty  times  the  surface  of  the  human  body. 

Fig.  7- 


1.  The  larynx;  2.  The  trachea;  3.  Right  bronchia;  4.  Left 
bronchia;  5.  Left  lung  divided  into  three  lobes;  7.  Large  bronchial 
tubes ;  8.  Small  bronchial  tubes  ending  in  air  cells  or  vesicles. 

13.  Such  is  the  structure  of  the  vessel  which  conveys  the 
air  to  the  blood ;  let  us  examine  how  the  blood  gets  to  the 
air.  This  is  effected  by  means  of  the  pulmonary  artery, 
which  springs  from  the  right  ventricle  of  the  hearty  divides 


248  PHYSIOLOGY. 

into  two  branches,  one  for  each  lung,  and  again  subdivides, 
and  ramifies  through  the  organ  in  a  manner  precisely  simi- 
lar to  the  bronchial  tubes.  Every  bronchus,  or  branch  of 
the  trachea,  thus  has  a  corresponding  blood-vessel,  which 
tracks  it  throughout  its  entire  course  until  it  reaches  the  air 
vesicles,  upon  the  surface  of  which  the  minute  vessels  ex- 
pand and  ramify,  forming  a  net-work  so  beautiful,  that  the 
anatomist  who  first  observed  it,  called  it  the  rete  mirahile,  or 
the  wonderful  net-work.  Thus  the  air  is  on  one  side,  and 
the  blood  on  the  other,  of  an  immense  surface  of  membrane, 
finer  than  the  most  delicate  lace  or  gauze  ;  and  as  such 
membranes  are  permeable  to  air  and  other  gases,  the  oxygen 
of  the  air  penetrates  it  and  unites  with  the  blood,  while  a 
portion  of  carbon  and  water  are  given  off  by  exhalation. 
Thus  does  the  blood  lose  its  dark  venous  character,  and  as- 
sume a  florid,  arterial  hue,  and  become  fitted  to  carry  life 
and  vigour  to  every  part  of  the  system. 

14.  Thus  we  see  that  th€  lungs  and  all  their  complicated 
^machinery  of  bones,  ligaments,  muscles  and  cartilages,  were 
formed  for  the  sake  of  these  little  air-cells  ;  for  it  is  through 
their  agency  that  the  blood  undergoes  the  necessary  changes 
and  alterations.  When  we  reflect  upon  the  relative  extent 
of  the  actual  respiratory  surface,  compared  with  the  dimen- 
sions of  the  lungs  themselves,  that  a  stratum  of  blood  seve. 
ral  hundred  feet  in  surface,  is  exposed  to  a  stratum  of  air 
still  more  extensive,  and  all  compressed  within  the  compass 
of  a  few  inches,  we  are  filled  with  admiration  and  astonish- 
ment at  the  wisdom  displayed  in  such  a  structure,  and  search 
in  vain,  among  all  the  contrivances  of  human  skill  and 
genius,  for  a  counterpart  1 

15.  We  are  now  prepared  to  trace  the  successive  acts  of 
respiration,  accomplished  through  the  agency  of  the  me- 
chanism just  described.  About  one  second  and  a  half  after 
expiration,  the  muscles  of  inspiration  begin  to  act,  the  inter- 
oostals  contract,  and,  by  elevating  the  ribs,  increase  the  dis- 
lance  between  the  spine  and  sternum.     As  the  ribs  rise,  the 


RE&PIRATION. 


249 


diaphragm  descends,  and  thus  the  cavity  of  the  chest  is  en- 
larged in  every  direction.  This  expansion,  like  that  of  a 
bellows,  causes  a  vacuum,  and  as  the  lungs  are  passive,  the 
air  consequently  rushes  in  through  the  mouth  and  nostrils 
to  fill  it,  and  this  influx  of  air  continues  until  the  density  of 
the  internal,  is  equal  to  that  of  the  external  air,  when  the 
act  of  inspiration  is  at  an  end.  Again,  the  intercostal 
muscles  relax,  and  the  ribs,  by  their  elasticity,  are  restored 
to  their  natural  position,  while,  at  the  same  moment,  the  dia- 
phragm relaxes,  and  allows  the  abdominal  muscles  to  con- 
tract and  thrust  it  up  into  the  chest.  Thus  the  lungs  being 
pressed  upon  in  every  direction,  below  by  the  diaphragm, 
before  by  the  sternum  and  ribs,  and  behind  by  the  spine  and 
ribs,  the  air  within  them  is  pressed  out  Such  is  the  beau- 
tiful and  complicated  mechanism  of  respiration. 

Fig.  8. 


The  cut  upon  the  left  represents  the  natural  shape  of  the  chest,  and 
that  upon  the  right,  the  contracted  state  of  it,  owing  to  tight  lacing. 

16.  Now  we  can  ea&ily  understand  how  tight-lacing  alters 
the  shape  and  diminishes  the  capacity  of  the  chest.  By 
looking  at  the  cut,  we  see  that  the  figure  of  the  chest  is  that 
of  an  irregular  cone,  with  a  convex  projection  on  each  side, 
and  flattened  before  and  behind.  By  con»pressing  it,  how- 
ever, by  corsets,  it  is  changed  into  a  cylinder,  its  lower  part 
feeing  forced  in,  so  that  its  transverse  diameter  is  diminished 


250  PHYSIOLOGY. 

nearly,  or  quite,  one  half.  Now,  in  this  state  of  things,  it 
is  very  clear  that  the  ribs  cannot  be  raised  upwards  and 
outwards,  as  they  are  in  natural  and  free  respiration,  and, 
consequently,  the  capacity  of  the  chest  cannot  be  enlarged 
in  these  directions.  How,  then,  is  life  supported  ?  Clearly 
by  the  play  of  the  diaphragm  alone,  which,  by  its  descent, 
enlarges  the  cavity  of  the  chest  in  its  long  diameter.  But 
even  the  action  of  this  muscle  is  cramped  by  this  unnatural 
practice  ;  for,  as  the  compressing  apparatus  extends  down 
over  the  loins  behind,  and  in  front  over  all  the  soft  parts,  or 
the  organs  below  the  chest,  it  acts  like  a  solid  wall,  prevent- 
ing, by  its  resistance,  the  protrusion  of  these  organs,  and 
thus  restrains  the  diaphragm  above,  in  its  attempt  to  de- 
scend ;  so  that  in  fact,  the  beautiful  mechanism,  contrived 
by  a  Supreme  architect,  for  performing  a  function  indispen- 
sable to  life,  health,  beauty  and  enjoyment,  is  confined, 
in  every  direction,  and  life,  consequently,  sapped  at  its  very 
fountain  head ! 

17.  If  an  opening  be  made  into  the  cavity  of  the 
chest,  the  lung  upon  that  side  immediately  collapses,  and  is 
no  longer  useful  in  breathing.  How  is  this  explained  ?  The 
lungs  have  a  constant  tendency  to  collapse,  and  they  are 
only  kept  from  doing  so,  by  the  pressure  of  the  air  contained 
within  them.  If  a  hole  be  made  in  the  walls  of,  the  chest, 
so  as  to  allow  the  atmospheric  air  to  come  in  contact  with 
the  external  surface  of  the  lungs,  and  thus  make  the  pressure 
on  the  external  and  internal  surface  equal,  they  immediately 
collapse  and  shrink  to  that  size  which  is  natural  to  them, 
and  which  they  assume  when  removed  from  the  chest.  This 
operation,  of  opening  the  cavity  of  the  chest,  has  been  pro- 
posed as  a  remedy  for  consumption  ;  as  the  lung  in  a  state 
of  rest  would  be  more  likely  to  heal  than  when  in  constant 
motion. 

18.  The  atmosphere  is  an  invisible  elastic  fluid,  surround- 
ing the  earth  to  the  height  of  about  forty  miles.  Water  is 
seven  hundred  times  heavier  than  air ;  and  yet  a  column  of 


RESPIRATION.  251 

air  a  foot  in  diameter,  and  extending  to  the  top  of  the  at- 
mosphere, would  be  equal  in  weight  to  a  column  of  water  of 
the  same  diameter  thirty-two  feet  high,  or  to  a  column  of 
mercury  twenty-eight  inches  high.  The  pressure  of  the  at- 
mosphere then,  upon  the  body  of  a  common  sized  man,  is 
equal  to  between  thirty  and  forty  thousand  ijounds.  Atmos- 
pheric air  is  composed  of  oxygen,  azote  and  carbonic  acid, 
in  the  proportion  of  20  parts  of  oxygen,  78  of  azote,  and  2 
of  carbonic  acid. 

19.  Oxygen  is  an  invisible  air,  or  gas,  and  enters  into  the 
composition  of  air,  water,  and  all  animal  and  vegetable  sub- 
stances. It  is  the  supporter  of  combustion,  and  no  animal 
can  live  without  it.  What  are  called  acids  and  oxyds  in 
chemistry,  are  oxygen  combined  with  other  substances,  as 
sulphur,  salt,  nitre,  &cc.  Azote  can  neither  support  combus- 
tion nor  respiration,  at  least  in  man ;  though  it  is  an  ele- 
ment in  all  animal  matter,  and  in  some  vegetables.  In 
these  cases  it  is  obtained,  both  from  food  and  the  air. 

20.  It  is  now  fully  ascertained,  that  while  the  chemical 
composition  of  the  blood  is  essentially  changed,  its  weight 
always  remains  the  same  ;  as  the  carbon  discharged  is  pre- 
cisely equal  to  the  united  weight  of  the  oxygen  and  azote 
absorbed,  and  the  same  change  is  effected  by  the  respiration 
of  all  animall,  whatever  be  their  rank  in  the  scale  of  organ- 
ization. It  is  worthy  of  remark,  that  plants  and  animals 
produce  directly  opposite  changes  in  the  chemical  constitu- 
tion of  the  air.  The  carbonic  acid  given  off  by  animals  is 
composed  of  oxygen  and  carbon  ;  this  is  decomposed  by 
vegetables,  which  absorb  the  carbon  and  give  off  the  oxygen 
to  the  air,  which  in  its  turn  is  absorbed  by  animals,  and  car- 
bonic acid  given  off:  so  these  two  great  departments  of 
organized  structure  furnish  food  for  each  other,  renovating 
the  air,  and  preserving  it  in  a  state  of  constant  purity.  The 
immense  quantity  of  oxyen  given  off  by  vegetables,  may  be 
inferred  from  the  following  experiment.  About  fifty  leaves 
were  enclosed  in  a  jar  of  air  ;  the  surface  of  the  whole  being 


.  252  PHYSIOLOGY. 

about  SOO  square  inches  ;  by  adding  some  carbonic  acid  t& 
the  jar,  in  a  short  time  26  cubic  inches  of  oxygen  were 
evolved..  What  then  must  be  the  amount  given  off  by  an 
entire  tree,  especially  in  cities,  where  carbonic  acid  abounds  ; 
hence  how  important  it  is  that  cities  should  be  thickly  plant- 
ed with  trees,  not  only  for  the  sake  of  ornament,  but  much 
more  for  that  of  utility. 

21.  The  quantity  of  oxygen  consumed  by  a  man  in  a 
minute,  is  about  30  cubic  inches.  He  breathes  20  times  in 
a  minute  ;  and  every  time  he  breathes^  takes  into  his  lungs  15 
cubic  inches  of  atmospheric  air^  which  contains  three  cubic 
inches  of  oxygen,  so  that  one  half  of  that  which  is  inspired 
disappears  in  every  act  of  respiration.  This  will  amount  ta 
about  2,000  cubic  inches  in  an  hour,  and  45,000  cubic  inches 
in  24  hours.  Thus  one  man  will  consume,  in  24  hours,  all 
the  oxygen  contained  in  a  space  o/"  312  square  feet ;  or  in  12 
hours,  in  156  square  feet.  And  still  our  churches,  and  school- 
rooms, and  dwelling-houses,  are  constructed  with  no  view  to 
a  renovation  of  the  air  we  breathe  ! 

22.  Dr.  Southwood  Smith  has  lately  performed  a  series 
of  very  interesting  experiments,  from  which  he  deduces  the 
following  general  results  : — "  1.  The  volume  of  air  ordinarily 
present  in  the  lungs  is  about  12  pints.  2.  The  volume  of 
air  received  by  the  lungs  at  an  ordinary  inspiration  is  one 
pint.  3.  The  volume  of  air  expelled  from  the  lungs  at  an 
ordinary  expiration,  is  a  little  less  than  one  pint.  4.  Of  the 
volume  of  air  received  by  the  lungs  at  one  inspiration^  only 
one-fourth  part  is  decomposed  at  one  action  of  the  heart,  and 
this  is  so  decomposed  in  the  five-sixth  parts  of  one  second 
of  time.  5.  The  blood  circulates  through  the  system,,  and 
returns  to  the  heart  in  160  seconds  of  time,  which  is  exactly 
the  time  in  which  the  whole  volume  of  air  in  the  lungs  is  de- 
composed. These  circuits  are  performed  every  eight  minutes ; 
540  circuits  are  performed  every  24  hours.  6.  The  whole 
volume  of  air  decomposed  in  24  hours  is  221,882  cubic  inches, 
exactly  540  Times  the  volume  of  the  contents  of  the  lungs. 


RESPIRATION.  253 

7-.  The  quantity  of  blood  that  flows  to  the  lungs  to  be  acted 
upon  by  the  air  at  one  action  of  the  heart  is  two  ounces,  and 
this  is  acted  on  in  less  than  one  second  of  time.  8.  The 
quantity  of  blood  in  the  whole  body  of  the  human  adult  is 
24  pounds  avoirdupois,  or  20  pints.  9.  In  24  hours  57 
hogsheads  of  air  flow  to  the  lungs.  10.  In  the  same  time, 
24  hogsheads  of  blood  are  presented  in  the  lungs  to  this  quan- 
tity of  air.  11.  In  the  mutual  action  that  takes  place  be- 
tween these  quantities  of  air  and  blood,  the  air  loses  328 
ounces  of  oxygen,  and  the  blood  10  ounces  of  carbon." 

23.  The  blood,  as  it  goes  the  round  of  the  system,  leav- 
ing a  little  bony  matter  here,  a  little  muscular  there ;  sup- 
plying the  nails,  and  the  hair,  and  the  skin,  and  every  thing, 
with  the  particles  which,  in  the  wear  and  tear  of  the  ma- 
chine, they  have  lost ;  loses  by  degrees  its  bright  arterial 
colour,  and  by  the  time  it  comes  round  again  to  the  lungs, 
it  is  no  longer  fit  to  perform  its  duty  ;  it  has  been  robbed  of 
all  its  principles  most  essential  to  life,  and  it  must  be  re- 
newed and  prepared  afresh,  before  it  can  be  of  any  further 
use.  This  is  done  in  the  lungs  :  and  this  process  is  what' 
physiologists  call  the  vital  part  of  respiration, 

24.  All  animals  have  not  lungs.  Insects  absorb  the  air 
from  the  surface  of  the  body ;  so  also  do  many  of  the  family 
of  zoophytes.  Some  have  feathery  tufts,  like  a  plume  of 
feathers,  which  they  keep  in  constant  motion ;  while  the 
common  earth-worm,  or  angle-worm,  has  a  single  row  of 
holes  along  its  back,  about  one  hundred  and  twenty  in  num- 
ber, which  open  each  of  them  into  a  small  respiratory  bag, 
situated  between  the  skin  and  the  intestine.  The  leech  or 
blood-sucker,  and  the  lamprey  eel,  have  the  same  kind  of 
apparatus  for  breathing. 

25.  In  fishes,  the  gills,  which  are  their  lungs,  are  made  up 
of  an  infinite  number  of  little  fibres,  or  filaments,  set  close 
together,  like  the  teeth  of  a  fine  comb,  or  the  barbs  of  a 
feather ;  and  these  are  covered  with  innumerable  small 
processes,  crowded  together  like  the  nap  of  velvet,  and  over, 

22 


254 


PHYSIOLOGY. 


these  are  spread  myriads  of  blood-vessels,  like  a  fine  net- 
work. The  air  which  is  contained  in  the  water,  is  drawn 
in  with  it  by  the  mouth,  and  forced,  by  the  muscles  of  the 
throat,  through  the  opening  leading  to  the  gills,  the  filaments 
of  which  are  expanded  and  separated  by  the  same  process, 
so  that  they  receive  the  full  action  of  the  fluid  as  it  passes 
by  them.  When  a  fish  is  taken  out  of  water,  the  reason  he 
cannot  breathe  is,  that  these  filaments  collapse,  and  adhere 
together  in  a  mass,  and  the  air  cannot  separate  them. 

26.  The  seal,  porpoise,  dolphin  and  whale,  belong  to  the 
class  mammalia,  and  therefore  have  to  rise  to  the  surface  of 
the  water  to  get  air  to  breathe.  It  is  this  necessity  which 
exposes  the  whale  to  the  harpoon  of  the  fisherman ;  for 
such  are  his  strength  and  swiftness,  that,  could  he  live  en- 
tirely under  water,  he  might  defy  the  utmost  ingenuity  of 
man  to  capture  him. 

Fig.  &. 


The  above  cut  shows  the  mode  of  respiration  in  fishes.  The  gills 
are  seen  bent  over  in  the  form  of  a  feather :  d  is  the  auricle  of  the 
heart;  e,  the  ventricle;  f,  the  bronchial  artery  ;  g,  g,  the  gills.    The 


RESPIRATION.  255 

Jieart  of  a  fish  throws  the  blood  only  to  the  gills,  and  not  to  the  rest  of 
the  body  as  in  other  animals.  This  is  the  reason  why  the  gills  are  red, 
while  the  other  parts  of  a  fish  are  white.  Respiration  in  fishes  is, 
therefore,  performed  by  taking  water  into  the  mouth,  and  forcing  it 
through  the  gills  ;  in  this  manner  the  air  contained  in  the  v/ater  is 
brought  in  contact  with  the  thin  coats  of  the  blood-vessels,  through 
which  the  oxygen  is  absorbed. 


Questions. — What  is  meant  by  respiration  ? — by  inspiration  ?— by 
expiration?  How  are  the  parts  concerned  in  respiration  arranged? 
What  bones  are  concerned  ?  Describe  the  position  of  the  ribs.  What 
muscles  are  chiefly  concerned  in  respiration  ?  Describe  the  intercos- 
tals, — the  diaphragm.  How  does  the  diaphragm  act  in  inspiration  ? 
In  expiration  ?  What  causes  the  deecent  of  the  ribs  in  expiration  ? 
Describe  the  structure  of  the  lungs.  What  called  in  the  lower  animals  ? 
What  are  the  pleuras  ? — the  mediastinum  ?  How  many  compartments 
is  the  chest  divided  into  ?  In  whicli  is  the  heart  ?  What  is  the 
trachea  ?  What  does  it  end  in  ?  How  large  are  the  air  cells  ?  What 
is  the  office  of  respiration  ?  What  amount  of  surface  do  the  air  cells 
present  ?  How  does  the  blood  get  in  contact  with  the  air  ?  Describe 
the  process  of  respiration.  How  does  tight  lacing  injure  the  health  ? 
What  happens  if  a  hole  is  made  into  the  cavity  of  the  chest  ?  What 
is  the  weight  of  the  atmosphere  equal  to  ?  Of  what  gases  is  it  com- 
posed ?  What  effect  do  vegetables  have  on  air  ?  What  is  oxygen  ? — 
azote?  What  is  the  effect  of  respiration  on  air?  How  much  oxygen 
is  consumed  by  a  man  in  twenty-four  hours  ?  How  do  insects  breathe  1 
— the  earth-worm  ? — fishes  ? — birds  ? — the  whale  ?  &c. 


CHAPTER  XIX. 

THE    CIRCULATION    OF    THE    BLOOD. 

1.  That  the  blood  is  constantly  circulating  throughout 
the  human  body,  was  unknown  till  Harvey  made  the  disco- 
very, two  hundred  years  ago.  Before  this  time,  air  was 
supposed  to  circulate  through  the  arteries',  or  air  tubes ; 
hence  their  name.  The  reason  why  this  great  truth  was 
not  found  out  sooner,  was,  that  on  examining  dead  bodies, 
the  arteries  were  always  found  empty  of  blood  ;  owing  to 
the  contractile  force  with  which  they  are  endowed. 

2.  The  circulation  is  called  one  of  the  vital  functions, 
because  it  is  essential  to  life.  Its  suspension  for  a  short 
time  throughout  the  body  is  certainly  fatal.  Hence  we  find 
that  diseases  of  the  heart  and  great  vessels  are  apt  to  tenni- 
nate  in  sudden  death,  while  in  other  diseases  the  approach 
of  death  is  gradual. 

3.  Life,  in  all  the  organs,  is  maintained  by  the  presence 
of  arterial  blood.  Without  it  they  could  not  be  nourished, 
nor  could  they  perform  their  appropriate  functions.  The 
moment  any  part  of  the  body  is  deprived  of  blood,  from  that 
time  it  ceases  to  grow ;  it  withers  and  decays,  and  soon  be- 
comes a  mass  of  dead  matter.  If  the  arteries  which  supply 
any  of  the  limbs  with  blood  are  tied,  the  limb  soon  grows 
black,  and  mortifies.  In  the  same  way,  if  we  stop  the  cir- 
culation of  sap  in  a  tree  by  girding  or  dividing  the  vessels 
which  convey  this  fluid  to  the  branches,  the  tree  immediate- 
ly dies.  Blades  of  grass  and  corn  are  often  destroyed  by 
worms  severing  the  same  vessels  with  their  teeth ;  and 
peach  and  other  fruit  trees,  are  generally  short  lived  from 
the  same  cause. 

4.  Some  animals  are  destitute  of  a  circulation,  such  as  in- 
sects, worms,  &c.  Air  and  food  are  essential  to  the  existenca 


THE    CIRCULATION    OF    THE    BLOOD.  257 

of  life,  but  the  food  cannot  be  changed  into  blood  before  the 
air  has  acted  on  it  by  one  of  its  principles,  oxygen.  Now, 
if  these  two  principles  are  not  introduced  into  the  system  in 
the  same  place,  but  in  separate  organs,  it  is  evident  they 
cannot  be  employed  in  nutrition  till  they  are  brought  toge- 
ther ;  which  is  done  in  the  lungs  ;  the  blood  is  there  fitted 
to  carry  nourishment  and  life  to  every  part  of  the  system. 
Every  animal  then,  that  has  a  local  respiration,  must  also 
have  a  circulation. 

5.  The  organs  of  the  circulation  are  the  heart,  arteries, 
the  veins,  and  the  capillary  vessels.  The  arteries  and  veins, 
or  the  arterial  and  venous  systems  as  they  are  called,  have 
been  compared  to  two  trees,  the  one  scarlet  and  the  other 
purple,  whose  trunks  are  united  at  the  heart,  and  whose 
branches  are  connected  at  their  extremities,  thus  forming  a 
regular  circle.  The  blood  is  then  forced  out  of  the  heart 
by  the  contraction  of  that  organ,  into  the  arteries,  by  which 
it  is  distributed  throughout  the  body  ;  from  whence  it  is  re- 
turned  by  the  veins.  Between  the  ends  of  the  arteries  and 
the  commencement  of  the  veins,  are  the  small  hair-like  ves. 
sels  called  capillaries. 

6.  The  heart  is  a  hollow  organ  of  a  muscular  and  fibrous 
structure,  and  somewhat  conical  in  shape.  It  is  placed  in 
the  fore  part  of  the  cavity  of  the  chest,  inclined  to  the  left 
side.  It  rests  on  the  midriff  or  diaphragm,  which  is  the 
muscle  that  separates  the  chest  from  the  abdomen  ;  and  it  is 
supported  also  at  its  base  which  is  uppermost,  by  means  of 
the  large  blood-vessels  connected  with  it.  The  heart  is  sur- 
rounded by  a  strong  membranous  bag,  called  the  pericar- 
dium,  by  which  it  is,  in  a  measure,  protected.  This  bag  is 
the  seat  of  dropsy  of  the  heart,  and  is  generally  found  to 
contain  more  or  less  water  after  death. 

7.  In  the  human  species,  and  throughout  the  class  mam-f 
malia,  the  heart  is  a  double  organ  ;  consisting  in  fact  of  two 
single  hearts,  each  of  which  gives  motion  to  a  different  kind 
of  blood.     One  of  these,  the  right  heart,  receives  the  dark 

23* 


258 


PHYSIOLOGY. 


venous  blood  which  is  returned  from  all  parts  of  the  body, 
and  sends  it  through  the  lungs,  from  whence  it  returns  to 
the  left  side  of  the  heart  changed  to  bright  arterial  blood, 
and  is  distributed  by  the  aorta,  or  great  artery,  through  the 
system.  The  right  heart  then  may  be  called  the  venous  or 
^pulmonary  heart,  the  left,  the  arterial  heart.  Both,  however, 
are  so  united  together,  as  to  form  in  appearance  but  one 
heart. 

Fig.  1. 


"View  of  the  heart  inclosed  in  its  bag,  or  pericardium,  which  is  a  se- 
rous membrane.     It  is  here  laid  open  and  turned  back. 

8.  Each  of  these  hearts  has  two  separate  cavities  ;  one  to 
receive  the  blood,  and  the  other  to  pump  it  out.  The  cavi- 
ties  which  serve  as  receptacles,  are  called  awicles,  those. 


THE    CIRCULATION    OF    THE    BLOOD.  259 

which,  by  contracting,  force  it  out,  are  called  ventricles. 
The  walls  of  the  heart  are  composed  of  strong  muscular  or 
fleshy  fibres,  crossing  and  interlacing  one  another,  and  those 
of  the  ventricles  are  much  thicker  than  those  of  the  auri- 
cles. 

9.  The  cavities  in  the  right  side  of  the  heart  are  trian- 
gular  in  shape,  and  those  of  the  left,  oval.  Each  cavity 
will  hold  about  two  ounces  of  blood.  Between  each  of 
these  two  cavities  or  chambers,  there  is  a  passage,  which  is 
closed  with  a  valve ;  so  that  when  the  ventricles  contract, 
the  blood,  instead  of  passing  through  into  the  auricle,  is 
poured  into  the  arteries.  This  valve  is  formed  by  the  dou- 
bling of  a  thin,  transparent  membrane,  which  lines  the 
cavities,  and  extends  both  through  the  veins  and  arteries. 
The  valve  in  the  right  side  of  the  heart  is  called  tricuspid, 
and  that  in  the  left,  bicuspid  or  mitral. 

10.  There  are  also  valves  placed  at  the  orifice  of  the 
great  arteries  of  the  heart,  the  pulmonary  and  aorta,  as  they 
are  given  off  from  the  right  and  left  ventricles.  They  differ 
somewhat  from  the  former,  by  being  of  a  half-moon  or  semi- 
lunar shape,  and  formed  by  folds  of  the  lining  membrane  of 
the  jirteries.  These  are  called  sigmoid  valves  ;  and  their 
use  is  to  prevent  the  blood  from  flowing  back  from  the  arte- 
ries into  the  ventricles.  Where  the  vena  cava,  or  the  great 
vein  which  returns  all  the  blood,  empties  into  the  right 
auricle  of  the  heart,  there  is  another  valve,  called  the  Eusta- 
chian valve.     (See  Fig.  2.) 

11.  The  arteries  are  the  vessels  into  which  the  blood  is 
immediately  propelled  by  the  action  of  the  heart,  and  which 
distribute  it  to  all  the  parts  of  the  body.  The  pulmonary 
artery  or  the  artery  of  the  right  side  of  the  heart,  circulates 
dark-coloured  or  venous  blood  through  the  lungs,  where  by 
exposure  to  the  air,  it  becomes  a  bright  scarlet.  This  is  re- 
turned into  the  left  auricle,  which  forces  it  into  the  left  ven- 
tricle, whence  it  is  sent  through  the  aorta  to  every  part  of 
the  system. 


260 


PHYSIOLOGY. 
Fig.  2. 


—^9 


View  of  the  heart  with  its  several  chambers  exposed  and  the  ves- 
sels in  connection  with  them.  1.  The  superior  vena  cava.  2.  The 
inferior  vena  cava.  3.  The  chamber  called  the  auricle.  4.  The  right 
ventricle.  5.  The  line  marking  the  passage  between  the  two  cham- 
bers, and  the  points  of  attachment  of  one  margin  of  the  valve.  6.  The 
septum  between  the  two  ventricles.  7.  The  pulmonary  artery,  arising 
from  the  right  ventricle,  and  dividing  at  8  into  right  and  left,  for  the 
corresponding  lungs.  9.  The  four  pulmonary  veins,  bringing  the  blood 
from  the  lungs  into  10,  the  left  auricle.  11.  The  left  ventricle.  12. 
The  aorta,  arising  from  the  left  ventricle,  and  passing  down  behind  the 
heart,  to  distribute  blood  to  every  part  of  the  system.  Thus  the  blood 
moves  in  a  double  circle,  one  from  the  heart  to  the  body,  and  from  the 
body  back  to  the  heart,  called  the  systemic  circle ;  the  other,  from 
the  heart  to  the  lung,  and  from  the  lung  back  to  the  heart,  called  the 
pulmonic  circle. 

12.  The  arteries  are  very  strong  and  elastic,  of  a  yellow- 
ish white  colour,  and  have  three  coats,  the  outer  one  of  which 
is  called  cellular,  the  middle,  the  fibrous  coat,  and  the  inter- 
nal, serous.  It  is  very  important  that  arteries  should  be 
elastic  and  capable  of  stretching,  because,  if  they  were  not, 
every  time  a  limb  was  broken,  the  artery  would  be  ruptured, 
and  the  person  bleed  to  death.     (See  Fig.  3.) 

13.  The  veins  which  return  the  blood  to  the  heart  consti- 
tute two  systems  like  the  arteries ;  the  one  brings  all  the 
dark-coloured  blood  from  the  head,  trunk  and  limbs,  and  in- 
ternal organs,  to  the  right  side  of  the  heart,  into  which  it 
opens  by  the  two  great  trunks,  called  the  upper  and  lower 


THE    CIRCULATION    OF    THE    BLOOD. 
Fig.  3. 


261 


The  Arterial  system. 

vena  cava.  The  other  conveys  the  scarlet-coloured  or  arte- 
rial blood,  from  the  lungs  to  the  left  auricle,  into  which  it 
issues  by  four  large  trunks,  called  imlmonary  veins.  The 
veins  are  strong;  and  flexible,  but  not  elastic  like  arteries. 
They  are  furnished  with  little  valves  placed  at  short  dis- 
tances from  each  other,  so  as  to  prevent  the  blood  from  flow- 


262  PHYSIOLOGY. 

ing  back  again.     Like  the  arteries,  they  are  supplied  with 
nerves  from  the  great  sympathetic  nerve. 


Portion  of  an  artery,  showing  the  several  coats  of  which  it  is  com- 
posed, separated  from  each  other.  1.  The  internal  or  serous  coat ;  2. 
The  middle  or  fibrous  coat;  3.  The  external  or  cellular  coat.  \ 

i 

14.  The  capillary  system.,  so  called  from  the  vessels  being 
small,  like  hairs,  presents  two  modifications.  The  first  con- 
sists  of  little  tubes,  furnished  with  proper  coats  or  walls, 
which  are  the  termination  of  the  arteries  and  the  commence- 
ment of  the  veins.  But  a  part  of  these  small  vessels  do  not 
terminate  in  veins,  but  in  the  very  substance  of  the  flesh, 
and  the  organs  themselves.  These  are  even  smaller  chan- 
nels than  the  first,  and  permit  only  a  single  globule  of  blood 
to  pass  out  at  a  time.  They  are  probably  formed  by  the 
fine  arterial  vessels,  gradually  losing  their  proper  coats,  and 
becoming  confounded  with  the  cellular  tissue. 

15.  In  the  capillary  system,  the  functions  of  secretion, 
nutrition,  absorption  and  calorification,  or  the  production  of 
animal  heat,  are  performed.  It  is  often  divided  into  two 
sections,  the  general  and  the  pulmonary.  The  first  has  al- 
ready been  described.  The  other  exists  only  in  the  lungs, 
and  connects  the  pulmonary  arteries  and  veins.  In  this  the 
blood  is  changed  from  venous  to  arterial. 

16.  The  account  which  has  been  given  of  the  circulation 
applies  to  the  human  species,  mammalia  and  birds.  Reptiles 
have  but  one  heart,  containing  one  ventricle  and  one  or  two 


THE  CIRCULATION  OF  THE  BLOOD.        263 

auricles,  which  receive  arterial  blood  from  the  lungs,  and 
venous  blood  from  the  body,  and  in  its  cavity  both  are 
mixed  together.  The  main  artery  going  from  the  heart,  di- 
vides into  two  branches,  one  of  which  goes  to  the  lungs,  the 
other  is  distributed  throughout  the  body.  In  some  of  the 
other  classes  of  animals,  such  as  worms,  there  is  no  heart, 
and  the  circulation  consists  in  the  passage  of  the  blood  from 
the  surface,  where  are  seated  the  organs  of  respiration,  to 
all  parts  of  the  animal  and  back  again,  which  is  performed 
exclusively  by  vessels.  Fishes  have  a  single  heart,  designed 
only  to  circulate  venous  blood,  which  it  conveys  to  the  gills, 
or  lungs ;  and  from  thence  it  is  carried  to  every  part  of  the 
body,  by  an  artery  which  rises  from  the  gills  themselves. 
Shell-fish  have  also  a  single  heart,  bat  this  only  circulates 
arterial  blood. 

17.  The  following  facts  were  brought  forward  by  Harvey 
to  prove  the  circulation  of  the  blood.  If  the  chest  of  a 
cold-blooded  animal  be  opened,  the  heart  will  be  seen  dilating 
and  contracting.  The  valves  are  so  situated  throughout  the 
circulating  system,  as  to  promote  the  circulation.  Between 
the  auricles  and  ventricles  they  are  so  placed  as  to  allow  the 
blood  to  pass  freely  from  the  former  into  the  latter,  and  to 
prevent  its  return.  The  valves  placed  at  the  orifice  of  the 
arteries,  permits  the  blood  to  enter  them  from  the  ventricles, 
but  prevents  it  getting  back  into  the  heart.  The  valves  in 
the  veins  allow  the  blood  to  go  towards  the  heart,  but  pre- 
vent it  from  going  in  the  other  direction. 

18.  In  bleeding,  a  bandage  or  ligature  is  placed  round  the 
arm,  above  the  point  where  the  arm  is  to  be  opened.  The 
blood,  in  its  return  toward  the  heart,  is  interrupted,  but  the 
artery  which  carries  the  blood  to  it  is  not  compressed,  be- 
cause  it  lies  deeper.  Sometimes,  however,  the  ligature  is  so 
tight  that  the  blood  will  not  flow  till  it  has  been  loosened. 
If  the  vein  be  opened  below  the  ligature  it  will  bleed  freely, 
but  no  blood  is  obtained  if  it  be  opened  above. 

19.  When  a  limb  is  amputated  by  a  surgeon,  he  only  ties 


264 


PHYSIOLOGY. 


the  arteries.  The  reason  is,  that  as  these  convey  the  blood 
from  the  heart,  the  patient  would  soon  bleed  to  death  unless 
some  means  were  adopted  to  prevent  it.  -But,  although  the 
veins  are  as  large  as  the  arteries,  yet,  as  they  carry  the 
blood  back  to  the  heart,  they  do  not  bleed,  although  they  are 
not  tied. 

Fig.  5. 


The  Venous  System. 


THE    CIRCULATION    OF    THE    BLOOD.  265 

20.  The  blood  can  also  be  seen  to  move  in  the  small  caj 
pillaries  by  means  of  a  microscope.  The  fine  web  of  a"* 
frog's  foot  is  generally  used  for  this  purpose.  Microscopi- 
cal observations,  however,  should  be  received  with  great  al- 
lowance, for  no  two  observers  have  ever  found  the  same  ap- 
pearances. One  makes  out  the  globules  of  the  blood  to  be 
TOund,  another  square,  and  another  tubular.  Some  physi- 
ologists, it  is  to  be  feared,  find  just  what  they  wish  to  find. 
Owing  to  the  refraction  of  light,  the  microscope  is  little  to 
be  depended  on  in  examining  the  minute  structure  of  bodies* 

21.  The  motion  of  the  blood  is  chiefly  owing  to  the  ac- 
tion of  the  heart.  This  contracts  with  great  force,  and  in 
the  following  manner.  The  auricles  both  contract  at  the 
same  instant,  forcing  the  blood  which  is  received  from  the 
lungs,  and  the  general  circulation,  into  the  ventricles  ;  these 
then  contract  at  the  same  moment ;  the  right  one  sending 
the  blood  through  the  lungs,  the  left  one  through  the  aorta. 
This  alternate  action  is  constant,  as  long  as  life  continues. 
The  reason  why  the  auricles  act  together,  and  the  ventricles 
the  same,  is  probably  owing  to  the  fact,  that  both  have  a 
common  septum  or  dividing  wall,  so  that  one  cannot  contract 
without  the  other. 

22.  The  ventricles  contract  more  suddenly  and  powerfully 
than  the  auricles,  and  they  are  three  times  as  long  in  dila- 
ting or  expanding,  as  contracting.  When  the  ventricles 
contract,  the  apex  or  point  of  the  heart  rises  up  and  strikes 
against  the  left  wall  of  the  chest,  between  the  sixth  and 
seventh  ribs,  and  this  can  be  felt  by  placing  the  hand  on  the 
left  side.  The  left  ventricle  has  much  thicker  and  stronger 
walls  than  the  right,  because  it  has  a  greater  distance  to 
throw  the  blood  ;  but  the  right  ventricle  will  hold  more  than 
the  left,  because  the  venous  system  is  more  capacious  than 
the  arterial. 

23.  The  velocity  of  the  blood  in  the  arterial  system  grows 
slower  in  proportion  to  its  distance  from  the  heart,  while 
that  in  the  veins  is  accelerated  the  nearer  it  approaches  the 

23 


266  PHYSIOLOGY. 

heart.  The  reason  why  the  blood  moves  slower  in  the  arte- 
ries as  it  recedes  from  the  heart,  is  owing,  probably,  to 
friction,  and  the  increased  capacity  of  the  vessels,  for  the 
arterial  system  is  compared  to  a  cane,  whose  apex  is  at  the 
heart.  The  course  of  blood  in  the  arteries  is  intermittent^ 
or  by  jets ;  not  that  it  does  not  flow  all  the  time,  but  its  flow 
is  more  or  less  rapid,  according  as  the  ventricles  are  con- 
tracting or  dilating. 

24.  The  force  with  which  the  blood  is  thrown  from  the 
heart  is  variously  estimated.  Hales  computed  that  the  left 
ventricle  of  a  horse  exerted  a  force  equal  to  J 13  pounds,  and 
that  of  a  man  at  51  pounds.  Some  think  that  the  contrac- 
tion must  overcome  the  whole  pressure  of  the  air  upon  the 
body,  which  is  equal  to  forty  thousand  pounds.  As  we  can- 
not, however,  correctly  estimate  the  influence  of  breathing 
and  other  causes,  we  cannot,  with  any  degree  of  certainty, 
tell  what  degree  of  power  is  exerted  by  the  heart.  Ih*. 
Arnott  thinks,  however,  that  the  heart  acts  with  a  force  of 
about  six  pounds  on  every  square  inch,  and  as  the  left  cham- 
ber of  the  heart  has  about  ten  square  inches,  the  whole  force 
exerted  is  sixty  pounds. 

25*  The  Blood, — The  blood  is  not  necessarily  red,  it  may 
be  white,  as  in  the  fish ;  transparent,,  as  in  the  insect ;  yel- 
lowish, as  in  the  reptile ;  and  indeed  there  is  no  animal  in 
which  the  blood  is  red  in  all  the  parts  of  its  body. 

26.  In  a  short  time  after  blood  is  taken  from  the  body  it 
separates  into  two  portions,  by  a  process  called  coagulatioHf 
▼iz.  1.  a  watery  portion  called  serum,  and  a  solid  portion 
called  coagulum  or  cht ;  the  white  substance  which  forms 
the  upper  part  of  the  clot  is  called  fibrin,  and  the  red  mass 
under  it,  the  red  particles.  The  fibrin  is  the  material  from 
which  all  the  solids  of  the  body  are  formed.     (See  Fig.  6.) 

27.  The  red  particles  owe  their  colour,  it  is  supposed,  to 
the  presence  of  iron ;  though  some  say  it  depends  on  an  ani- 
mal substance  of  a  gelatinous  nature.  These  are  usually 
described  as  being  minute  globules^  but  the  latest  microsco- 


THE  CIRCULATION  OF  THE  BLOOD. 

Fig.  6. 


267 


A  portion  of  fibrin,  showing  its  fibrous  structure  and  the  net-like 
arrangement  of  its  fibres. 

pic  observations  show  that  they  are  flattened  cakes,  having 
rounded  and  slightly  thickened  margins,  as  shown  in  the 
following  cut  4 

Fig.  7. 


1.  A  particle  of  human  blood  as  it  appears  when  transparent  and 
iloating.  2.  The  same,  seen  as  illuminated.  3.  The  same,  one  half 
illuminated.  4.  A  particle  of  frog's  blood  floating.  5.  The  same, 
seen  edge-wavs.  All  these  objects  are  magnified  five  hundred  diam- 
eters. 

28.  The  blood  constitutes  about  one  fifth  part  of  the 
weight  of  the  whole  body;  so  that  the  whole  quantity  of 
blood  in  the  body  of  an  adult  may  be  estimated  at  between 
thirty  and  forty  pounds.  A  complete  revolution  of  the 
blood  takes  place  every  tJu-ee  minutes,  and  there  are  about 
five  hundred  and  fifty  revolutions  every  twenty-four  hours. 
The  contractions  of  the  ventricles,  or  the  pulse,  is  about 
seventy-five  times  in  a  minute,  in  a  grown  person,  and  one 
liundred  and  forty  in  an  infant ;  in  old  age  about  sixty. 


268  PHYSIOLOGY. 

Now  as  two  ounces  of  blood  are  thrown  out  of  the  heart  at 
each  beat,  thirty -Jive  pounds  on  an  average,  must  pass  through 
the  heart  every  three  minutes  ;  seven  hundred  pounds  every 
hour ;  and  sixteen  thousand  pounds,  or  eight  tons,  every 
twenty-four  hours. 

29.  Dr.  Barry  states,  that  the  quicker  the  blood  circu- 
lates the  sooner  will  the  machine  wear  out.  Now,  suppose 
that  the  pulse  of  a  temperate  man  be  seventy  in  a  minute, 
and  by  the  use  of  ardent  spirits  he  forces  it  up  to  eighty- 
five,  then  instead  of  living  seventy  years,  his  number  of  pul- 
sations will  be  finished  at  the  age  of  fifty-six  ;  thus  cutting 
short  his  life  fourteen  years, 

30.  The  heart  beats  more  than  one  hundred  thousand 
times  in  twenty. four  hours,  and  sometimes  continues  to  beat 
thus  for  one  hundred  years.  What  other  machine  so  comb- 
plicated,  could  last  as  long  ?  And  still  it  is  made  of  nothing 
but  flesh.  How  strange  that  it  should  act  so  long,  without 
growing  weary  !  Truly  is  it  said,  that  "  man  is  fearfully  and 
wonderfully  made !" 

31.  Some  physiologists  consider  the  heart  the  only  mo- 
ving power  of  the  circulation  :  Others  think  that  the  arte- 
ries aid  by  their  contractile  power.  Others  still  believe  that 
the  capillary  vessels  have  a  kind  of  absorbing  and  propelling 
force,  independent  of  the  heart  and  arteries,  while  a  last 
class  ascribe  the  circulation  to  a  self-moving  power  in  the 
blood  itself.  All  these  theories  may  have  some  truth  in  them, 
but  they  err  in  being  too  exclusive. 

32.  That  the  heart  is  the  chief  moving  power  of  the 
blood  is  generally  admitted.  If  the  heart  of  a  frog  be  ta- 
ken from  the  body  and  placed  in  warm  water,  it  will  con- 
continue  to  contract  and  dilate  with  great  force  for  a  con- 
siderable time.  This  would  seem  to  prove  that  its  action 
does  not  depend  on  the  contact  of  air  and  blood.  In  ser- 
pents the  heart  retains  this  power  a  long  time  after  death; 
and  it  iias  been  known  to  contract  at  least  four  days  after 
life  appeared  extinct.     The  heai't  of  a  sturgeon  was  cut  out 


THE    CIRCULATION    OF    THE    BLOOD.  269 

and  laid  on  the  ground,  and  after  it  ceased  to  beat  it  waa 
blown  up  and  ordered  to  be  dried.  It  was  then  hung  up, 
when  it  began  to  move  again  and  continued  to  beat,  though 
more  slowly,  for  ten  hours  ;  and  it  continued  to  contract  till 
it  became  so  dry  as  to  rustle  with  the  motion.  If  the  heart 
of  any  animal  be  taken  from  the  body  immediately  after 
death  and  carefully  washed,  it  will  continue  to  act  for  some 
time  ;  showing  that  this  alternation  of  action  is  natural  to 
its  irritable  fibre,  and  results  directly  from  its  structure. 

33.  The  arteries  have  not  an  equal  power  of  contraction, 
with  the  heart,  though  they  are  generally  found  more  or  less 
contracted  after  death.  The  pulse,  which  may  be  felt  by 
placing  the  fingers  on  the  side  of  the  wrist,  takes  place  at 
the  very  instant  the  heart  contracts,  and  is  not  probably 
owing  to  the  contraction  or  dilitation  of  the  artery,  but 
chiefly  to  the  jet  of  blood,  which  is  sent  along  the  tube. 
When  arteries  are  changed  into  bone,  the  pulse  is  still  felt* 
No  pulse  exists  in  animals  destitute  of  a  heart. 

34.  That  the  arteries  are  not  only  elastic,  but  contract  s© 
as  to  assist  the  heart  in.  circulating  the  blood,  is  evident  from 
the  following  facts.  If  an  artery  be  laid  bare,  and  two  lig- 
atures applied  so  as  to  cut  off"  all  communication,  and  then 
^  small  opening  made  between  the  ligatures,  the  blood  will 
spirt  out  with  considerable  force,  and  the  artery  become 
much  contracted.  When  a  person  or  animal  is  bleeding  to 
death,  the  arteries  always  contract  in  proportion  to  the  loss 
of  blood  ;  after  death  they  relax  again.  Arteries  too  wiU 
contract  by  the  application  of  stimulants  or  irritating  sub^ 
stances. 

35.  Besides  these  facts  to  prove  that  arteries  contract, 
We  may  mention  the  following.  We  read  of  cases  of  pal- 
sy, where  in  the  paralytic  limb  no  pulse  could  be  felt,  al- 
.though  the  heart  beat  as  strongly  as  ever.  We  read  of  oth- 
er cases  where  the  arteries  continued  to  beat  after  the  pul- 
sations of  the  heart  ceased.  In  diseases  of  the  heart,  we 
sometimes  have  a  weak  pulse,  although  the  heaj't  beats  very 

23* 


279  FHYSIOLOGY. 

stroi^ly.  And  in  apoplexy  the  pulse  is  often  strong,  when 
the  heart  acts  feebly.  Burns  relates  cases  where  the  pulse 
at  the  wrist  did  not  correspond  with  the  contractions  of  the 
heart :  and  it  cannot  be  denied  that  in  some  animals  a  cir- 
culation exists,  although  they  have  no  heart.  Although  fish- 
es have  a  heart,  their  blood  is  moved  through  the  body  by 
vessels.  After  the  heart  is  ta>ken  out  of  the  body,  the  blood 
is  still  seen  to  flow  in  the  small  vessds. 

36.  I  have  stated  that  arteries  contract  by  an  irritating 
substance  being  applied  to  them.  Hartshorn,  or  ammonia, 
will  make  an  artery  shrink  so  as  to  lose  one  eighth  of  its  cir- 
cumference. A  partial  enlargement  of  an  artery  takes  place 
in  a  living  animal  by  exposing  it,  and  rubbing  ife  between 
the  finger  and  thumb,  but  in  general  no  pulsation  will  be 
seen  in  an  artery  thus  exposed, 

37.  The  capillary  vessels  have  an  action  independent  of 
the  heart.  When  the  blood  has  reached  the  ends  of  the  ar- 
teries, or  the  capillary  vessels,  the  force  of  the  heart  and  ar- 
teries is  probably  nearly,  if  not  quite  exhausted.  Dr.  Ar- 
nott  says  that  the  blood  is  driven  into  them,  by  a  force 
equal  to  four  pounds  to  the  square  inch.  There  is  no  doubt 
that  the  action  of  the  heart  is  sufficient  to  force  the  blood 
through  the  arteries  into  the  veins  ;  for  when  the  heart  acts 
feebly  the  surface  of  the  body  is  pale  and  cold.  But  the 
blood  is  known  to  move  in  a  backward  or  retrograde  direc- 
tion. When  a  leech  is  applied  to  the  skin,  the  blood  flows  to 
the  spot  from  all  quarters.  In  blushing,  the  capillaries  of 
the  cheek  dilate  instantly  and  admit  more  blood ;  under  the 
influence  of  fear  they  contract,  and  the  face  becomes  pale  ; 
tears  will  gush  from  the  eye  in  a  moment  and  suddenly  dis- 
appear ;  now  all  these  things  could  not  happen  if  these  ves- 
sels did  not  act  independent  of  the  heart. 

38.  It  is  probably  capillary  action  which  moves  the  fluids 
in  all  animals  that  have  no  heart.  Persons  have  lain  in  a 
swoon  apparently  dead  for  days  together  and  then  revived. 
In  these  cases  life  was  preserved  in  the  capillary  circulation. 


THE  CIRCUI*ATION  OF  THE  BLOOD.       271 

I  have  seen  a  case  of  this  kind,  where  a  young  lady  of  this 
city,  was  kept  a  fortnight  after  she  was  supposed  to  have 
died ;  her  looks  being  so  natural  that  her  parents  were  un- 
willing to  bury  her,  for  fear  she  would  come  to  life.  Al- 
though she  lay  in  a  room  without  a  fire  in  the  winter  season, 
yet  her  body  retained  its  natural  warmth  for  several  days, 
her  cheeks  their  florid  colour,  and  her  limbs  their  usual  flex- 
ibility^ These  singular  phenomena  were  perhaps  owing  to 
a  continuance  of  the  capillary  circulation, 

40.  The  capillary  vessels  are  the  last  part  of  the  body  that 
continues  to  act.  After  the  breathing  and  the  action  of  the 
heart  have  ceased,  they  still  continue  to  act  like  innumera- 
ble little  pumps,  drawing  the  blood  out  of  the  arteries  and 
substance  of  the  organs,  and  forcing  it  into  the  veins.  As 
nutrition  and  secretion  are  performed  by  that  portion  of  the 
capillary  system  which  acts  independently  of  the  heart  and 
arteries,  the  continuance  of  action  in  this  system  accounts 
for  the  growth  of  the  beard  and  the  hair,  which  takes  place 
after  death.  It  is  owing  to  the  same  reason,  that  the  arte- 
ries are  always  found  empty  after  death* 

41.  Physiologists  are  not  agreed  as  to  the  cause  of  the 
motion  of  blood  in  the  veins.  The  veins  have  thinner  coats 
than  the  arteries  and  are  destitute  of  elasticity.  As  they  are 
wanting  in  elasticity,  if  they  had  no  irritability,  they  could 
not  act  upon  the  blood  contained  in  them,  and  accordingly 
could  exert  no  active  force  in  circulating  the  blood.  But  it 
is  found  by  experiments  that  the  veins  are  not  mere  passive 
tubes.;  they  possess  a  certain  degree  of  contractile  power,  as 
is  shown  in  the  shrinking  of  the  veins  on  the  back  of  the 
hands  in  cold  weather ;  besides,  if  a  vein  be  punctured  be- 
tween two  ligatures,  the  blood  will  spirt  out.  The  veins 
then  assist  the  circulation  by  a  sli  ht  degree  of  contractile 
power. 

42.  Again  :  when  the  heart  dilates,  the  blood  is  sucked 
up  in  the  veins  precisely  as  it  is  in  a  pump.  This  is  denied 
hy  some,  who  saj,  that  if  the  end  of  a  syringe  be  placed  in  a 


272  PHYSIOLOGY. 

tube  of  eel-skin,  or  any  thing  which  is  not  elastic,  and  you 
attempt  to  pump  the  water  out  of  it,  supposing  it  to  be  filled, 
the  sides  will  be  brought  together,  and  the  tube  closed,  so 
that  the  water  cannot  escape.  This,  however,  will  not  hap- 
pen, if,  as  in  the  veins,  the  fluid  is  forced  in  at  the  other  end. 

43.  The  expansion  of  the  chest  in  breathing,  also  aids  in 
circulating  the  blood  in  the  veins.  When  the  chest  is  dila- 
ted, both  air  and  blood  rush  into  it.  This  may  be  seen  by 
watching  the  jugular  veins  in  the  neck,  which  empty  them- 
selves during  inspiration.  Dr.  Barry  placed  one  end  of  a 
tube  in  the  jugular  vein,  and  the  other  in  a  coloured  fluid. 
During  inspiration,  the  fluid  was  sacked  from  the  vessel  into 
the  vein  ;  during  expiration,  it  remained  stationary.  It  should 
be  remembered,  that  during  one  act  of  respiration,  the  heart 
beats  five  or  six  times. 

44.  One  other  cause  remains  to  circulate  the  blood  in  the 
veins,  and  that  is,  the  action  of  the  muscles.  When  the 
muscles  contract,  they  press  upon  the  veins  in  contact  with, 
or  near  them,  and  so  force  the  blood  along  their  cavities* 
This  can  be  seen  in  bleeding  from  the  arm ;  if  a  person 
grasps  a  stick,  the  blood  flows  much  more  freely  than  when 
the  muscles  are  relaxed.  It  is  in  this  way,  that  exercise 
proves  so  beneficial  to  health,  by  promoting  the  circulation 
of  the  blood  through  the  system  ;  and  we  account  in  this 
way  also,  for  the  fact  that  sedentary  habits  so  often  lay  the 
foundation  for  incurable  diseases. 

45.  The  heart  is  not  so  dependent  on  the  brain  for  its  ac- 
tion as  many  other  organs.  Monsters,  born  without  heads, 
sometimes  live  for  several  days.  Snakes  have  lived  six 
months  without  a  head  ;  and  any  animal  may  live  for  some 
time  in  the  same  condition,  if  the  blood-vessels  of  the  neck 
are  tied.  If  the  breathing  be  kept  up  by  artificial  respiration, 
life  may  be  continued  for  a  long  time.  I  have  myself  kept 
a  child  alive  two  hours,  that  had  its  neck  broken,  by  keeping 
up  artificial  breathing  ;  persons  have  been  saved  in  the  same 
way,  who  had  taken  large  doses  of  laudanum. 


THE  CIRCULATION  OF  THE  BLOOB.       273 

46.  In  fainting,  the  heart  ceases  to  act.  It  may  be  owing 
to  various  causes,  acting  on  the  nervous  system,  or  on  the 
blood-vessels.  Mental  emotion,  loss  of  blood,  or  any  thing 
that  renders  the  blood-vessels  about  the  heart  less  full  or 
tense  than  usual,  will  cause  a  person  to  faint.  This  state  is 
soonest  relieved  by  lying  down,  probably  because  the  action 
of  the  heart  is  sufficient  to  force  the  blood  along  horizontal 
tubes,  but  not  to  raise  it  in  a  perpendicular  position.  Where 
blood  has  been  lost  in  sufficient  quantity  to  endanger  life,  it 
has  been  supplied  from  the  veins  of  another  person,  by  a  pro- 
cess called  transfusion. 


Questions. — "When  was  the  circulation  of  the  blood  discovered? 
and  by  whom  ?  Why  not  discovered  before  ?  Why  is  the  circulation 
called  a  vital  function  ?  How  is  life  maintained  ?  Have  all  animals 
a  circulation  ?  Describe  the  structui?e  of  the  heart.  What  is  the  peri- 
cardium ?  In  what  animals  is  the  h^art  double  ?  Describe  the  cavi- 
ties of  the  heart — the  valves.  What  is  their  use  ?  What  are  arteries  ? 
How  many  coats  have  they  ?  Describe  the  venous  system.  Have  the 
veins  valves  ?  What  is  the  capillary  system  ?  Describe  tlie  circulation 
in  reptiles — worms — fishes.  What  facts  did  Harvey  bring  forward  to 
prove  the  circulation  of  the  blood  ?  What  is  the  motion  of  the  blood 
chiefly  owing  to  ?  Are  the  ventricles  thicker  than  the  auricles  ?  Why  ? 
What  is  said  of  the  velocity  of  the  blood?  Of  the  force  of  the 
heart  ?  Describe  the  composition  of  the  blood  ?  What  proportion  of 
the  body  does  it  constitute  ?  How  long  is  the  blood  in  performing  a 
revolution  ?  What  is  the  last  part  of  the  body  that  continues  to  act  ? 
Why  are  the  arteries  found  empty  after  death?  What  circulates  the 
blood  in  the  veins  '?  What  aids  in  this  process  ?  Does  the  heart  de- 
pend  on  the  brain  for  its  action  ?  What  facts  connected  with  this  sub- 
ject ?  What  occurs  in  fainting  ?  What  position  is  most  favorable  to 
recovering  from  fainting  ? 


CHAPTER  XX. 

Ts^UTRITIVE    FUNCTIONS. — DIGESTION. 

1.  Digestion^  absorption,  secretion,  and  nutrition  constitute 
what  are  called  the  nutritive  functions.  Digestion  is  that 
process  by  which  the  food  is  brought  into  a  state  in  which 
it  may  be  taken  up  by  the  lacteal  vessels  and  carried  into 
the  blood.  The  digestive  apparatus  consists  of  the  mouth 
and  its  appendages  ;  the  pharynx  ;  esophagus  ;  the  st&inach 
and  intestines ;  the  whole  tract  making  what  is  called  the 
alimentary  canal.  Besides  these,  there  are  the  salivary 
glands  ;  the  liver ;  the  pancreas,  or  sweet-bread  of  animals ; 
all  of  which  aid  in  tha  process  of  digestion. 

2.  The  parts  which  compose  the  mouth,  are  the  lips, 
cheeks,  palate,  tongue,  teeth,  and  salivary  glands.  There  are 
six  salivary  glands,  which  secrete  saZiva,  viz.:  the  parotid; 
suh.maxillary ;  and  the  sub-lingual.  The  parotid  gland  is 
situated  on  the  cheek  before  the  ear ;  the  sub -maxillary  im- 
mediately beneath  the  lower  jaw  ;  and  the  sub-lingual  under 
the  tongue.  They  all  pour  forth  a  fluid,  during  mastication, 
into  the  mouth  to  moisten  the  food,  and  prepare  it  for  the 
change  it  is  to  undergo  in  the  stomach.  A  swelling  of  the 
parotid  gland  is  called  the  mumps, 

3.  In  a  grown  person,  there  are  thirty-two  teeth  ;  four  in- 
cisor, or  cutting  teeth,  two  canine  or  dog  teeth,  ten  molar  or 
grinders  in  each  jaw.  The  first  set  of  teeth  begin  to  come^ 
when  the  child  is  about  six  months  old,  and  by  the  time  it  is 
two  years  and  a  half  old,  it  has  twenty ;  about  the  seventh 
year,  they  all  become  loose  and  fall  out,  and  their  place  is 
supplied  by  another  set.  The  teeth  are  the  hardest  part  of 
the  body ;  their  internal  parts  resemble  bone ;  the  external 
consist  of  a  very  hard  and  highly  polished  substance,  called 
enamely  which  is  very  durable. 


NUTRITIVE     FUNCTIONS DIGESTION.  275 

Fig.  1. 


7p  £  ^       I 

\  i     A       /-N 


Half  of  the  lower  jaw  ;  a,  the  base  j  6,  the  angle  ;  c,  the  ramus ;  <f, 
the  condyle ;  e,  the  coronaid  process ;  h,  the  two  incisors  or  cutting 
teeth ;  z,  one  canine  or  dog  tooth ;  A:,  two  small  molar ;  Z,  three  large 
molar  or  grinding  teeth. 

4.  The  jaws  perform  an  important  part,  in  fitting  the  food 
for  the  stomach.  The  lower  jaw  only  has  motion  f  being 
moved  by  means  of  strong  muscles,  which  rise  from  the  tem- 
ples and  upper  jaw  ;  and  it  not  only  moves  directly  upwards 
and  downwards,  but  sideways,  so  as  to  grind  the  food  be- 
tween the  teeth,  as  grain  is  ground  between  two  mill-stones. 

5.  The  tcmgue  is  likewise  very  useful  in  the  process  of 
mastication,  as  it  removes  the  food  from  one  part  of  the 
mouth  to  another,  so  as  to  bring  every  portion  between  the 
teeth ;  and  then  it  forms  it  into  a  suitable  shape  for  swal- 
lowing. The  tongue  is  made  up  by  different  muscles,  and  is 
supplied  by  nerves,  chiefly  from  the  eleventh  ■pair. 

6.  The  esophagus  or  meat-pipe,  lies  directly  behind  the 
wind-pipe,  and  is  about  one  inch  in  diameter.  It  connects 
what  is  called  the  pharynx,  with  the  stomach.  All  these  or- 
gans are  lined  by  a  soft,  velvet-like  membrane,  termed  mucous 
membrane,  because  it  is  always  covered  in  health,  with  a  vi- 
scid fluid,  called  mucus. 


276 


PHYS'IOLOGT. 


7.  The  stomach  is  "the  largest  organ  of  digestion.  It  lie^ 
immediately  under  the  false  ribs,  on  the  left  side,  below  the 
midriff,  and  is  shaped  somewhat  like  a  bag-pipe.  It  has  two 
op^aings,  the  upper  one,  which  admits  the  food,  is  called  car- 
diac, and  the  lower  one,  the  pyloric  orifice.  In  a  middle  sized 
man,  this  organ  is  about  ten  inches  long,,  and  three  or  four  in 
diameter,  and  holds  from  three  to  six  pints. 

8.  The  stomach  has  four  distinct  coats  ;  the  inner  one  is 
called  mucous  or  villous ;  being  thin,  soft,  and  spongy  ;  the 
second  vascular ;  as  it  is  made  up  chiefly  of  blood  vessels ; 
the  third  muscular  \  composed  of  muscular  fibres,  and  very 
strong  ;  the  fourth  serous ;  as  it  secretes  a  serous  or  watery 
fluid.  The  stomach  is  freely  supplied  with  blood  vessels  and 
nerves;  the  latter  being  furnished  partly  from  the  spinal 
marrow,  and  partly  from  the  brain. 

Fiff.  2. 


The  human  stomach  :  a,  the  esophagus  or  gullet ;  h,  the  cardiac  por- 
tion ;  c,  the  left  extremity  ;  d,  the  small  extremity  ;  e,  the  pylorus  tied  ; 
g  g,  the  omentum  or  caul,  which  is  attached  to  the  outside  of  the 
stomach,  and  falls  over  the  intestines  like  a  curtain. 


NUTRITIVE    FUNCTIONS DIGESTION.  277 

9.  The  intestines  in  man,  are  from  five  to  six  times  the 
length  of  the  body  ;  and  are  divided  into  large  and  small  in- 
testines ;  the  latter  making  about  four  fifths  of  the  whole. 
The  small  intestines  are  divided  into  duodenum,  jejunum^ 
and  ileon.  The  duodenum  is  so  called  because  it  is  about 
twelve  finger's-breadth  in  length  ;  the  jejunum  from  its  gene- 
rally being  found  empty  ;  the  ducts  or  canals  from  the  liver 
and  pancreas  enter  the  duodenum  near  the  middle,  and  it  is 
abundantly  supplied  with  lacteals.  The  different  portions 
of  the  large  intestine  are  called  coecum,  colon,  and  rectum. 

10.  The  liver  is  the  largest  gland  in  the  body  ;  and  it  lies 
directly  under  the  ribs,  on  the  right  side,  and  reaching  be- 
low them.  In  a  grown  person,  it  is  about  ten  inches  in  diam- 
eter, and  weighs  not  far  from  four  pounds.  It  secretes  the 
hile,  which  is  poured  out  into  a  bag  called  gall-bladder,  con- 
nected with  it ;  from  thence  it  is  carried  into  the  duodenum. 
The  liver  is  found  in  all  the  vertehrated  animals  and  in  the 
mollusca ;  in  birds,  reptiles  and  fishes,  its  size  is  greater  in 
proportion  to  that  of  the  body  than  in  the  human  species. 
It  is  attached  to  the  diaphragm,  which  lies  above  it,  by  a 
fold  of  the  peritoneum,  called  the  suspensory  ligament  of  the 
liver. 

11.  The  'pancreas  is  a  gland  about  five  inches  in  length, 
of  a  whitish  colour,  lying  immediately  behind  the  stomach. 
It  is  supplied,  like  the  stomach,  with  numerous  blood-vessels 
and  nerves.  It  secretes  a  fluid,  called  the  pancreatic  Jluid, 
which  is  white,  viscid,  inodorous,  slightly  saline,  and  con- 
tains a  large  proportion  of  albumen.     This  gland  is  found 

•in  all  the  mammalia,  in  birds,  and  in  amphibious  animals,  or 
such  as  live  both  in  air  and  water,  like  the  frog  ;  but  it  is 
much  larger  in  animals  that  live  on  vegetables,  than  in  those 
that  feed  on  flesh.  Hence,  the  fluid  which  it  secretes,  is 
supposed  to  aid  in  difficult  digestion.     (See  Fig.  3.) 

24 


278 


PHYSIOLOGY. 
Fig.  3. 


The  above  cut  represents  the  whole  tract  of  the  intestinal  canal,  not 
exactly  in  its  natural  position,  but  spread  out  so  as  to  show  the  relative 
proportions  ;  /,  the  sesophagus ;  g,  cardia ;  h,  pylorus ;  i,  i,  the  duodenum, 
about  twelve  fingers'  breadth  in  length ;  k,  hepatic  duct ;  I,  gall  blad- 


NUTRITIVE    FUNCTIONS DIGESTION.  279 

■d-sr  ;  tn,  cystic  duct;  n,  ductus  communis,  formed  by  the  union  of  both; 
o,  the  opening  of  this  duct  into  the  duodenum ;  p,  pancreatic  duct ;  q, 
its  opening  into  the  duodenum;  r,  jejunum;  s,  ilium;  these  constitute 
the  small  intestines,  and  are  about  twenty-sLx  feet  in  length,  or  five 
times  the  length  of  the  body ;  t,  termination  of  ilium  in  the  coccum ; 
M,  superior  fold  of  valve  of  colon  ;  v,  inferior  do. ;  lo,  coecum  ;  x,  ver- 
miform process ;  y,  y,  colon ;  z,  rectum.  The  coecum,  colon,  and 
rectum,  form  the  large  intestines,  and  are  about  six  feet  in  length  ;  the 
coecum  being  about  4  inches  long,  and  the  same  in  diameter.  The 
arrows  show  the  direction  which  the  food  takes  in  digestion. 

12.  Hunger  and  thirst  are  sensations  designed  to  teach  us 
the  necessity  of  supplying  those  losses  which  the  system  is 
constantly  undergoing  by  the  different  secretions  and  excre- 
tions, amounting  to  several  pounds  in  the  course  of  twenty- 
four  hours.  The  blood  first  feels  the  loss,  and  then  the 
«olids,  whose  particles  are  continually  taken  up  by  the  ab- 
sorbents, and  carried  into  the  blood,  and  thus  ejected  from 
the  system ;  and  were  not  these  losses  supplied  by  the  timely 
introduction  of  food,  the  body  would  rapidly  emaciate,  till 
death  closed  the  scene.  Hunger  is  supposed  to  be  owing  to 
a  peculiar  affection  of  the  nerves  of  the  stomach ;  for  when 
the  nerve  which  goes  from  the  brain  to  the  stomach  (the  par- 
vagum,)  is  divided,  the  sensation  of  hunger  is  lost,  or  at 
least  the  appetite  for  food  is  destroyed. 

13.  While  the  food  is  undergoing  the  process  of  mastica- 
tion, that  is,  of  being  divided  and  ground  down  by  the  teeth, 
it  is  thoroughly  mixed  with  a  quantity  of  saliva,  amounting 
it  is  supposed  to  between  eight  and  ten  ounces.  The  food 
is  thus  brought  into  a  condition  to  be  easily  swallowed,  and 
readily  dissolved  by  the  action  of  the  stomach.  It  is  very 
important,  therefore,  that  the  food  should  be  slowly  chewed, 
and  reduced  to  as  fine  a  state  as  possible  in  the  mouth,  in 
order  that  digestion  may  be  easy.  Too  great  rapidity  in 
eating,  probably  lays  the  foundation  of  many  cases  of  indi- 
gestion. 

14.  After  the  food  has  been  sufficiently  masticated,  it  is 
can'ied  down  the  aesophagus  into  the  stomach,  first  by  the 


280  PHYSIOLOGY. 

contraction  of  the  muscles  of  the  'pharynx,  and  then  by  a 
successive  contraction  of  the  circular  fibres  of  the  gullet  it- 
self, from  above  downwards.  That  the  morsel  is  not  carried 
down  merely  by  its  own  weight,  is  proved  by  the  fact,  that 
a  man  can  swallow  with  his  head  downwards. 

15.  In  the  stonaach,  the  food  is  converted  into  a  soft,  grey, 
pulpy  mass,  called  chyme.  This  process  has  been  called 
chymosis.  It  is  produced  by  the  motions  of  the  stomach, 
together  with  the  agency  of  the  secretions,  which  are  thrown 
out  by  the  gastric  vessels.  These  motions  have  been  called 
'oermicular  or  worm-like ;  and  undulatory,  or  like  wave  suc- 
ceeding wave.  The  crawling  of  a  worm  furnishes  a  very 
good  illustration  of  the  successive  contractions  of  the  muscu- 
lar fibres  of  the  stomach,  commencing,  as  they  do,  at  the  seso- 
phagus,  and  proceeding  onwards  to  the  pylorus,  and  so  back 
again.  These  motions  of  course  bring  every  portion  of  the 
contents  of  the  stomach  in  contact  with  all  parts  of  its  sur- 
face ;  and  so  they  become  intimately  mixed  with  the  gastric 
fluid. 

16.  The  food  is  thus  carried  round  the  interior  of  the  sto- 
mach, from  one  extremity  to  the  other  ;  and  from  one  to 
three  minutes  are  employed  in  each  revolution.  In  the  mean 
time,  both  orifices  are  closed ;  so  that  the  contents  cannot 
escape.  During  this  process,  the  gastric  fluid  is  secreted  in 
large  quantities,  and  becomes  mixed  with  the  food  as  it 
passes  round.  In  a  short  time,  the  taste,  smell,  and  other 
sensible  properties  of  the  food,  are  entirely  changed.  This 
is  produced  by  the  agency  of  the  gastric  juice,  which  sub- 
verts the  chemical  affinities  of  the  food  ;  and  with  its  ele- 
ments forms  new  combinations. 

17.  The  gastric  fluid  is  a  clear,  transparent  fluid,  produced 
by  arterial  exhalation  ;  acid  to  the  taste,  slightly  saline,  and 
free  from  odour.  It  possesses  the  singular  property  of  co- 
agulating albumen ;  resists  the  putrefaction  of  animal  mat- 
ter ;  and  dissolves  nearly  every  kind  of  alimentary  substance. 
Its  acid  properties  are  owing  to  the  muriatic  and  acetic  acids 


NUTRITIVE    FUNCTIONS DIGESTION.  281 

which  it  contains.  The  gastric  fluid  is  found  to  contain 
more  acid,  in  proportion  as  the  food  is  more  difficult  of 
digestion.  It  is  only  secreted,  when  food  is  present  in  the 
stomach. 

18.  The  aliment  then  is  converted  into  chyme,  chiefly  by 
the  gastric  fluid ;  aided,  however,  by  the  motions  of  the  sto- 
mach. This  is  proved  by  the  fact,  that  this  fluid  will  dis- 
solve alimentary  substances  out  of  the  stomach  :  the  chyme 
which  is  prepared  by  artificial  digestion,  presenting  the  same 
sensible  properties  as  that  which  is  found  in  the  stomach. 
Such  is  the  power  of  the  gastric  fluid,  that  it  will  dissolve 
bones,  not  only  in  the  stomach,  but  out  of  it.  It  curdles 
milk ;  and  for  this  purpose  the  rennet,  or  stomach  of  the 
calf,  is  used  by  farmers  in  making  cheese.  But  every  thing 
which  is  coagulated  in  the  stomach,  is  dissolved  again,  in  its 
conversion  into  chyme.  t 

19.  But  digestion  is  a  vital  and  not  a  chemical  process. 
Though  aliment  may  be  reduced  to  a  substance  resembling 
chyme,  by  the  action  of  gastric  fluid  out  of  the  body ;  yet 
it  is  destitute  of  all  those  peculiar  properties  which  assimi- 
late it  to  the  nature  of  a  living  animal.  The  food  may 
doubtless  be  brought  to  a  fluid  state  by  a  chemical  process, 
and  even  alimentary  principles  may  in  the  same  way  be 
changed  into  each  other,  as  starch  into  sugar  and  gum;  but 
there  is  still  another  power,  which  may  be  called  vitalizing 
or  organization,  by  which  alimentary  substances  are  brought 
into  such  a  condition  as  adapts  them  for  an  intimate  union 
with  the  living  body.  Such  a  power  is  beyond  the  reach  of 
chemical  action. 

20.  The  time  which  is  required  to  change  food  into  chyme, 
varies  according  to  the  nature  of  the  food.  Animal  food  is 
digested  sooner  than  vegetable.  The  average  time  required, 
is  about  three  hours  and  a  half.  A  good  deal  depends,  also, 
on  the  degree  of  mastication  it  has  undergone.  If  swallowed 
in  large  masses  its  solution  must  go  on  slowly. 

21.  As  fast  as  the  aliment  is  changed  into  chyme,  it  pass- 

24* 


282 


PHYSIOLOGY. 


es  out  of  the  stomach  into  the  duodenum,  and  it  generally 
stays  in  the  stomach  until  it  has  undergone  this  change. 
Indigestible  substances  have  thus  been  vomited  up,  more 
than  a  week  after  they  were  swallowed.  All  fluids  which 
are  swallowed,  are  supposed  to  be  taken  up  by  absorption. 

22.  If  the  par.vagim,  or  nerve  which  goes  from  the  brain 
to  the  stomach,  be  divided,  digestion  is  impaired  or  suspend, 
ed.  The  same  happens  under  the  influence  of  mental  emo- 
tions,  such  as  grief,  anger,  &c.  Some  physiologists  have 
thought  that  this  nerve  presides  over  the  secretion  of  the 
gastric  juice ;  others,  that  it  stimulates  the  muscular  motions 
of  the  stomach ;  while  a  third  ckss  consider  it  to  be  the 
seat  of  sensation  in  the  stomach,  giving  rise  to  hunger  and 
thirst.  But  it  is  not  yet  fully  settled  what  particular  influ- 
ence this  nerve  exerts  over  digestion. 

23.  The  chyme,  on  passing  from  the  stomach,  is  received 
into  the  duodenum.     This,  like  the  stomach,  has  a  serous, 
muscular,  and  mucous  coat,  and  has  a  mucms,  as  well  as  se. 
rous,  secretion.     In  this  portion  of  intestine,  the  chyme  in 
its  passage  meets  with  the  pancreatic  and  the  biliary  fluids ; 
the  irritating  properties  of  the  acid   chyme,   cause  these 
fluids  to  be  poured  out  in  great  abundance,  as  well  as  the 
other   secretions  ;    and  these    are    thoroughly  mixed    with 
the  chyme  by  the  contraction  of  the  intestine.     It  now  be- 
comes  of  a  yellowish,  instead   of  a  gray  colour ;  its   acid 
properties  disappear,  and  large  quantities  of  albumen  are 
developed.     This  is  supposed,  by  some,  to  be  derived  from 
the  pancreatic  fluid,  which  contains  a  large  proportion  of  it. 
24.  As  it  becomes  intimately  mixed  with  the  biliary  and 
pancreatic  secretions,  the  substance  called  chyle  is  produced. 
Though  some  say  it  is  not  to  be  found  in  the  duodenum— but 
only  the  elements  out  of  which  it  is  formed.     But  albumen, 
which  IS  the  basis  of  chyle,  exists  abundantly  in  the  duode- 
num ;  and  so  also  do  particles  of  fibrin.     By  the  microscope, 
globules  also  may  be  detected  in  the  chyme,  similar  to  those 
which  are  found  in  the  chyle. 


NUTRITIVE    FUNCTION'S DIGESTION.  283 

25.  It  would  seem,  then,  that  the  great  business  of  diges. 
tion  is  to  change  the  food  into  albuminous  matter,  which 
forms  the  basis  of  the  chyle  as  well  as  the  blood  ;  and  it  is 
certain  that  no  albumen  is  formed  in  the  stomach ;  though 

.  the  change  which  the  food  there  undergoes,  is  an  approach 
to  the  nature  of  albumen.  As  the  bile  is  alkaline,  it  doubt, 
less  combines  with,  and  neutralizes  the  acid  properties  of 
the  chyme,  which  would  precipitate  the  miictis  of  the  bile, 
and  leave  it  in  a  state  of  coagulation. 

26.  Chyle  then  is  the  fluid,  which  is  taken  up  by  the  ab- 
sorbent  vessels,  called  lacteals,  whether  it  exists  ready  formed 
in  the  chyme,  or  is  manufactured  out  of  it,  by  the  action  of 
these  vessels  themselves.  It  is  usually  of  a  milk  white  co- 
lour,  but  varies  in  appearance  in  different  animals  ;  and  ac- 
cording to  the  nature  of  the  food.  In  animals  that  feed  on 
flesh,  it  is  opaque  ;  in  such  as  live  on  vegetables,  it  is  trans- 
parent ;  in  birds  and  fishes,  thin,  serous,  and  clear  like  wa- 
ter. It  is  saltish,  and  somewhat  sweet  to  the  taste  ;  heavier 
than  water  but  less  so  than  blood.  It  coagulates  on  stand- 
ing, like  blood,  and  separates  into  three  portions  ;  a  fluid,  a 
coagulum,  and  a  fatty  substance.  The  fluid  portion  is  chief. 
\y  of  albumen  and  coagulates  like  the  serum  of  the  blood  by 
heat,  acids,  and  alcohol ;  the  coagulum  consists  of  fibrin, 
and  a  coloring  matter,  which  is  white. 

27.  Whatever  the  food  may  consist  of,  physiologists  are 
now  pretty  well  agreed,  that  the  chyle  will  always  be  com- 
posed  orjibrin,  albumen,  a  fat  matter,  muriate  of  soda,  and 
phosphate  of  lime,  though  in  variable  proportions.  Food 
that  contains  much  azote,  such  as  that  of  animals,  it  is  sup. 
posed  will  form  chyle,  which  contains  a  greater  portion  of 

fibrin  than  that  of  vegetables,  as  azote  is  one  of  the  chief  ele- 
ments  of  fibrin.  Dr.  Marcet  states  that  chyle  produced  from 
vegetable  aliments  contains  three  times  as  much  carbon  as 
that  formed  out  of  animal  substances.  It  is  certain  that 
chyle  from  animal  food  is  milky  ;  and  that  from  vegetables 
transparent.     As  both  however  are  composed  of  the  same 


284  PHYSIOLOGY. 

essential  elements,  we  may  be  assured,  that  man  can  live  on 
either  animal  or  vegetable  diet,  as  it  may  be  most  conve- 
nient. As  the  most  important  part  of  digestion  seems  to  be 
<;ompleted  in  the  small  intestines,  we  shall  not  follow  the  pro- 
cess any  farther. 

28.  A  few  years  since,  a  man  in  the  United  States  army 
received  a  gun-shot  wound,  which  made  a  hole  in  his  sto- 
mach ;  and  which  left  an  opening  into  the  cavity  of  that  or- 
gan, so  that  the  whole  process  of  digestion  could  be  seen,  as 
it  was  going  on.  Dr.  Beaumont,  a  physician  in  the  army, 
availed  himself  of  this  singular  case,  and  performed  many 
curious  experiments  which  occupied  him  for  several  years. 
The  following  are  the  most  important  inferences,  which  he 
drew  from  his  experiments. 

29.  "  Animal  and  farinaceous  aliments  are  more  easy  of 
digestion  than  vegetables.  Digestion  is  facilitated  by  mi- 
nuteness of  division  and  tenderness  of  fibre ;  hence  the  im- 
portance of  thoroughly  chewing  the  food.  The  ultimate 
principles  of  aliment  are  always  the  same,  from  whatever 
kind  of  food  they  may  be  obtained,  whether  vegetable  or  an- 
imal. The  quantity  of  food  generally  taken  into  the  sto- 
mach, is  greater  than  the  system  requires.  Solid  food  is  ea- 
sier of  digestion  than  fluid.  Stimulating  condiments,  such  as 
spices,  are  hurtful  to  a  healthy  stomach. 

30.  The  continued  use  of  ardent  spirits  always  produces 
diseases  of  the  stomach.  Hunger  is  the  effect  of  the  dis- 
tension  of  the  vessels,  which  secrete  the  gastric  juice.  The 
temperature  of  the  stomach  is  100  degrees  of  Fahrenheit. 
The  gastric  juice  dissolves  the  food,  and  alters  its  properties. 
It  also  coagulates,  or  renders  solid,  albumen,  and  afterwards 
dissolves  it. 

31.  The  gastric  juice  is  a  clear  and  transparent  fluid  ;  a 
little  saltish,  and  somewhat  sour  to  the  taste.  When  pure, 
it  suffers  no  change  by  keeping.  Gentle  exercise  assists  the 
digestion  of  the  food.  Water,  ardent  spirits,  and  most  other 
fluids  are  not  affected  by  the  gastric  juice,  but  disappear 
from  the  stomach  soon  after  they  are  received." 


NUTRITIVE    FUNCTIONS DIGESTION.  285 

Questions. — ^WJiat  constitute  the  nutritive  functions  ?  What  the  di- 
gestive apparatus?  What  the  mouth?  How  many  sahvary  glands 
are  there  ?  How  many  teeth  are  there  in  an  adult  ?  How  divided  ? 
When  do  they  begin  to  appear  ?  When  are  they  shed  ?  What  is  the 
outside  of  the  tooth  called  ?  How  is  the  tongue  useful  in  mastication  ? 
Describe  the  esophagus — the  stomach — the  intestines — the  liver — the 
pancreas — hunger  and  thirst.  Describe  the  process  of  digestion.  What 
is  the  gastric  juice  ?  Chyme  ?  Chyle  ?  What  is  rennet — what  used 
for  ?  Is  digestion  a  chemical  process  ?  How  long  does  it  generally 
take  to  convert  food  into  chyme  ?  What  influence  has  the  par  vagum 
nerve  on  digestion  ?  Where  do  the  pancreatic  and  biliary  fluids  enter 
the  intestines  ?  their  use  ?  Is  the  nature  of  chyle  changed  by  the  kind 
of  food  ?  Of  what  is  it  always  composed  ?  What  are  the  principle  re- 
sults of  Beaumont's  experiments  in  relation  to  digestion  ? 


CHAPTER  XXI . 

SECRETION. 

1.  Secretion  is  one  of  the  most  obscure  and  mysterious 
functions  in  the  animal  economy.  To  secrete  means  to  sepa- 
rate  ;  but  most  of  the  fluids  formed  by  this  process,  did  not 
previously  exist  in  the  blood,  but  only  the  elements  out  of 
which  they  are  made.  It  is  purely  a  vital  and  not  a  inechan- 
ical  process,  like  straining  through  a  seive,  to  which  some 
have  compared  it :  and  the  vessels  by  which  it  is  accom- 
plished may  well  be  called  the  architects  and  chemists  of  the 
system  ;  for  out  of  the  same  material,  the  blood,  they  con- 
struct a  variety  of  wonderful  fabrics,  and  chemical  com- 
pounds. 

2.  We  see  the  same  wonderful  power  possessed  also  by 
vegetables — for,  out  of  the  same  materials,  the  olive  pre- 
pares its  oil ;  the  cocoa-nut  its  milk  ;  the  cane  its  sugar  ;  the 
poppy  its  narcotic  juice  ;  the  henbane  its  poison  ;  the  oak 
its  green  pulpy  leaves,  its  light  pith,  and  its  dense  woody  fi- 
bre :  all  composed  of  the  same,  few  simple  elements,  only  ar- 
ranged in  different  order  and  proportions. 

3.  In  like  manner,  we  find  the  vessels  in  animal  bodies, 
capable  of  forming  all  the  various  textures  and  substances 
whicti  make  up  the  frame ;  the  cellular  tissue ;  the  mem- 
branes ;  the  ligaments ;  the  cartilages  ;  the  bones  ;  the  mar- 
row ;  the  muscles,  with  their  tendons  ;  the  lubricating  fluid 
of  the  joints  ;  the  pulp  of  the  brain  ;  the  transparent  jelly  of 
the  eye  ;  in  short,  all  the  textures  of  the  various  organs  of 
which  the  body  is  composed ;  and  still  all  are  made  out  of 
the  same  blood ;  and  consist  of  the  same  ultimate  elements. 

4.  The  most  simple  form  of  secretion,  however,  seems  to 
be,  the  mere  separation  of  some  principle,  which  previously 
existed  in  the  blood  ;  as  serum  is  deposited  in  most  of  the  ca- 
vities, by  a  kind  of  exhalation.     Some  other  principles  also 


SECRETION.  287 

exist  in  the  blood,  which  are  found  in  the  secretions,  as  fi- 
brin, a  fatty  substance ;  and  some  of  the  elements  of  the 
bile.  Some  physiologists  believe,  that  many  of  the  secre- 
tions do  exist  ready  formed  in  the  blood,  but  cannot  be  de- 
tected by  analysis.  In  proof  of  this,  two  ounces  of  bile  have 
been  injected  into  the  veins  of  a  dog,  but  the  blood  of  the 
animal,  which  was  analyzed  a  few  moments  after,  exhibited 
not  a  trace  of  bile. 

5.  That  secretion  is  a  vital  process  and  not  a  chemical 
one,  is  evident  from  the  fact,  that  it  is  so  much  under  the 
influence  of  the  nervous  system.  For  example,  sorrow  and 
grief  change  the  qualities  of  the  bile :  a  fit  of  anger  some- 
times causes  an  excessive  flow  of  it :  it  will  also  change  the 
nature  of  milk  to  such  a  degree,  as  to  produce  colic,  vomit- 
ing, and  even  convulsions  in  the  infant  that  swallows  it. 
Grief  will  also  suspend  the  secretion  of  the  gastric  fluid,  and 
thus  destroy  the  appetite  ;  while  fear  causes  a  cold  sweat  to 
break  out,  all  over  the  surface  of  the  body.  If  the  nerves  go- 
ing to  any  organ  are  divided,  the  function  of  secretion  will 
be  suspended.  It  is  doubtless  owing  in  a  great  degree  to  the 
changeful  states  of  the  nervous  system,  that  the  secretions 
vary  so  much  in  quality  as  well  as  quantity  at  different  pe- 
riods. 

6.  Though  we  are  able  to  understand  but  little  of  the  true 
nature  of  secretion,  we  know  that  there  are  three  hinds  ofse- 
cretory  organs,  viz.,  exhalent  vessels ;  follicles  ;  and  glands. 
The  exhalents  are  believed  to  be  the  termination  of  the  arte- 
ries, or  capillaries  ;  and  they  are  of  two  kinds,  internal  and 
external ;  the  former  terminating  on  all  the  surfaces  within 
the  body ;  and  the  latter  on  the  outside.  Their  use  is  to 
soften  and  lubricate  these  parts. 

7.  The  fluid,  which  is  thrown  out  by  the  serous  mem- 
brane which  surrounds  the  brain,  the  lungs,  and  the  contents 
of  the  abdomen,  as  well  as  into  the  cavities  of  the  joints,  is 
very  similar  to  the  water  of  the  blood,  and  its  use  is,  to  keep 
the  parts  in  a  moist  state,  and  enable  the  organs  to  move  ea- 


288  PHYSIOLOGY. 

sily  on  each  other.  Fat  is  also  a  secretion^  which  is  thrown 
out  in  a  fluid  state,  from  the  cellular  tissue,  into  little  cells ; 
and  it  is  mostly  found  immediately  under  the  skin,  between 
that  and  the  flesh.  Its  use  seems  to  be,  to  lubricate  the  so- 
lids and  facilitate  their  movements  ;  to  form  a  cushion  around 
the  body^  and  protect  it  from  external  injuries  as  well  as  the 
extremes  of  heat  and  cold. 

8.  During  sickness,  when  we  take  little  or  no  food  into 
the  stomach,  life  is  supported  by  the  absorption  of  the  fat, 
which  is  taken  up  by  little  vessels  and  again  poured  into  the 
blood,  to  nourish  the  body ;  also  in  animals  which  lie  in 
their  burrows,  in  a  half  torpid  state  during  the  winter,  their 
nourishment  is  derived  from  the  same  source. 

9.  Marrow  which  fills  all  the  cavities  of  the  long  bones, 
is  very  much  like  fat,  and  this  also  is  a  secretion  from  a  thin, 
delicate  membrane,  that  lines  the  cavities  of  the  bones. 
These  are  the  principal  internal  exhalations,  or  secretions. 

1 0.  The  external  secretions  are  two  in  number ;  the  first 
and  most  important  from  the  skin  is  called,  when  insensible, 
perspiration ;  and  when  it  is  visible,  is  called  sweat ;  the  se- 
cond is  from  the  lungs,  and  can  be  seen  in  the  form  of  a  va- 
pour in  a  frosty  morning.  The  fluid  which  escapes  from  the 
skin,  is  chiefly  water,  containing  a  little  acid  and  some  salts, 
with  a  small  quantity  of  animal  matter. 

11.  The  skin  is  covered  with  an  innumerable  number  of 
pores,  so  small  indeed,  as  to  be  invisible  to  the  naked  eye, 
through  which  the  insensible  perspiration  is  constantly  pour- 
ing, amounting  in  weight  to  more  than  one  half  of  all  the 
food  and  drink  taken  into  the  stomach,  and  much  exceeding 
that  lost  by  all  the  other  excretions. 

12.  From  a  vast  number  of  experiments  performed  by  dif- 
ferent persons,  it  appears  that  the  largest  amount  of  insensi- 
ble  perspiration  amounts  to  five  pounds  in  twenty-four  hours, 
and  the  smallest  to  thirty-two  ounces.  Now,  when  we  con- 
sider that  the  skin,  serves  as  one  of  the  chief  outlets,  by 
which  the  old  and  useless  particles  are  got  rid  of,  out  of  the 


SECRETION.  289 

blood,  and  that  checked  perspiration  is  one  of  the  most  pow- 
erful causes  of  disease  and  death,  we  shall  see  how  important 
it  is  to  keep  the  pores  of  the  skin  free,  by  frequent  washing 
and  bathing  at  all  seasons  of  the  year. 

13.  When  the  surface  also  is  chilled  by  cold,  and  reaction 
does  not  follow,  the  blood-vessels  become  contracted  all  over 
the  skin,  and  the  blood  retreats  to  the  inner  parts  of  the 
body ;  the  29  ounces  of  waste  and  noxious  matter,  which 
ought  to  be  discharged,  are  kept  in  the  system,  and  sickness 
is  the  consequence.  Accordingly,  we  find  that  it  is  a  good 
remedy,  in  most  cases  of  disease,  to  excite  a  perspiration  and 
keep  it  up  for  some  time. 

14.  The  uses  of  transpiration  by  the  skin,  are,  not  only 
to  carry  out  of  the  body  the  noxious  properties  of  the  blood, 
but  also  to  render  the  skin  soft  and  pliable,  the  sense  of 
touch  delicate,  and  also  to  cool  the  body  when  exposed  to 
great  heat. 

15.  The  exhalation  from  the  lungs  closely  resembles  that 
from  the  skin.  It  was  once  supposed  to  be  formed  in  the 
lungs,  by  the  union  of  hydrogen  from  the  blood,  and  oxy- 
gen from  the  air,  thus  forming  water  ;  but  it  is  the  opinion 
of  most  physiologists  at  present,  that  it  is  either  the  watery 
part  of  the  mucus  secreted  by  the  mucous  coat  of  the  lungs 
and  air  passages,  or  that  it  is  given  off  directly  from  the 

blood. 

16.  The  Follicles,  are  small  sacks  or  bags,  found  in  the 
skin,  and  the  mucous  membranes.  The  pores  which  we  see 
on  the  skin  are  only  the  outlets  of  these  follicles.  Their  use 
is  to  secrete  an  oily  matter  to  mix  with  the  perspiration,  and 
help  to  keep  the  skin  soft  and  moist ;  when  these  outlets  are 
closed,  sometimes  there  appear  small  black  specks  on  the  skin, 
sometimes  called  worms,  but  they  are  nothing  more  than 
hardened  mucus.  Every  hair  has  a  follicle  at  its  root,  and 
the  wax  which  collects  in  the  ears,  is  secreted  by  follicles. 

17.  The  chief  agents  of  secretion  in  the  body,  are  the 
glands,  which  are  bodies  of  various  size,  generally  of  a 

25      . 


290  PHYSIOLOGY. 

rounded  form  ;  and  the  fluids  they  secrete,  are  very  diiferent 
from  each  other,  and  also  from  the  blood  which  furnishes  the 
same  materials  to  all.  For  instance,  the  liver  secretes  the 
yellow,  ropy  fluid,  called  bile  ;  the  kidneys,  secrete  urine ;  the 
lachrymal  gland,  which  is  placed  immediately  over  the  eye 
in  the  orbit,  secretes  the  tears  ;  and  the  spittle  or  saliva  is 
poured  out  from  the  salivary  glands. 

18.  Glands  are  formed  of  a  large  number  of  arteries,  veins, 
nerves,  and  lymphatics,  disposed  in  a  peculiar  manner,  and 
connected  together  by  a  tissue  of  cellular  membrane.  When 
in  a  cavity,  they  are  covered  on  their  external  surface  by  a 
coat,  derived  from  the  membrane  that  lines  the  cavity,  and 
they  are  also  provided  with  a  canal,  called  excretory  duct, 
which  is  lined  with  mucous  membrane.  There  are  seven 
kinds  of  glandular  secretions. 

19.  The  secreted  fluids  have  been  divided  into  serous  on 
watery,  albuminous  mucous,  oily,  and  the  mixed  ;  such  as  sa- 
liva, bile,  tears,  &c.  They  have  also  been  divided  into  recre. 
mentitiotis  and  the  excrementitious,  or  those  which  are  des- 
tined to  be  absorbed  and  returned  into  the  mass  of  the  blood, 
and  which  are  deposited  in  cavities  that  have  no  external 
opening ;  and  the  second,  those  which  are  designed,  after 
their  formation,  to  be  expelled  from  the  system. 

20.  When  any  substance  is  taken  up  by  the  absorbents, 
and  carried  into  the  blood,  which  cannot  be  converted  to  any 
useful  purpose  in  the  system,  it  is  immediately  discharged  by 
means  of  the  secretions.  Not  many  years  ago,  a  man  was 
carried  into  a  London  hospital,  who  was  picked  up  drunk  in 
the  streets.  He  lived  but  a  short  time,  and  on  examining 
his  brain,  nearly  a  half  a  gill  of  fluid  strongly  impregnated 
with  gin,  was  found  in  the  ventricles.     This  was  secreted. 

21.  Unless  the  secretions  all  go  on,  we  cannot  enjoy  good 
health.  If  that  from  the  skin  is  stopped,  fever,  or  some  in- 
ternal inflammation  is  the  consequence.  If  the  bile  ceases 
to  flow,  we  cannot  properly  digest  our  food ;  and  so  if  any 
of  the  others  are  interrupted,  some  serious  disease  will  be  the 


SECRETION.  291 

result.     The  use  of  ardent  spirits  deranges  all  the  secretions, 
and  this  is  one  reason  why  they  shorten  life  so  much. 


Questions. — What  is  Secretion  ?  Is  it  a  vital  process  ?  Have  vege- 
tables the  same  property  of  secretion  ?  Illustrate  this.  What  is  the  use 
of  this  function  ?  What  is  the  most  simple  form  of  secretion  ?  How 
is  it  proved  that  secretion  is  a  vital  process  ?  How  many  kinds  of  se- 
cretory organs  are  there  ?  What  are  exhalents  ? — their  use  ?  What 
is  fat?  How  is  life  supported  in  sickness  ?  What  is  marrow  ?  What 
are  the  external  secretions  ?  How  much  does  the  insensible  perspira- 
tion amount  to  in  24  hours  ?  What  important  inference  do  we  derive 
from  this  in  relation  to  health  ?  What  is  use  of  transpiration  by  the 
skin  ?  What  is  the  exhalation  from  the  lungs  owing  to  ?  What  are 
follicles  ?  What  are  the  chief  agents  of  secretion  ?  What  are  glands 
composed  of  ? — their  structure  ?  How  are  the  secreted  fluids  divided  ? 
What  becomes  of  useless  substances  carried  by  absorption  into  the 
blood  ?  Can  health  be  maintained  if  the  secretions  be  checked  ? 


CHAPTER  XXII. 

ABSORPTION. 

1.  Absorption  is  another  function  of  the  animal  body, 
immediately  connected  with  nutrition.  By  it  is  meant  that 
process  by  which  food  and  drinks,  designed  for  the  nourish- 
ment and  growth  of  the  body,  are  taken  up  and  carried  into 
the  blood  ;  and  also  those  particles  and  materials  that  have 
been  already  deposited,  and  have  become  either  useless  or 
injurious,  are  conveyed  into  the  general  mass  of  the  circula- 
ting fluids,  and  thus  removed  from  the  system.  The  first  is 
effected  by  the  lacteal  vessels ;  the  second  by  the  lymphatics, 

2.  The  absorbent  system,  so  called,  consists  of  the  lym- 
phatic  vesselSf  the  lymphatic  glands,  and  the  thoracic  duct. 
The  lymphatic  vessels  arise,  not  only  from  all  the  mucous 
surfaces,  but  also  from  the  whole  surface  of  the  body ;  the 
intimate  tissue  of  every  structure  ;  and  from  all  cavities, 
such  as  the  chest,  abdomen,  the  joints,  the  pericardium,  and 
even  the  ventricles  of  the  brain.  They  are  exceedingly 
small  at  their  origin,  but  by  uniting,  form  larger  and  larger 
trunks  as  they  proceed,  which  is  generally  in  the  course  of 
the  veins,  till  they  finally  discharge  their  contents,  either  in- 
to the  thoracic  duct,  or  some  of  the  large  veins  near  the 
heart.  Throughout  their  whole  extent,  they  are  provided 
with  numerous  valves,  which,  when  they  are  distended  with 
lymph,  causes  them  to  resemble  a  string  of  beads. 

3.  Every  part  of  the  body  is  supposed  to  be  furnished 
with  absorbent  vessels,  with  the  exception  of  the  nails,  the 
hair,  the  cuticle,  and  the  enamel  of  the  teeth.  And  even  in 
these,  it  is  not  impossible  that  they  may  exist ;  only  they 
are  too  small  to  be  detected. 

4.  The  lymphatics  of  the  small  intestines,  called  lacteah^ 
are  the  agents  of  digestive  absorption.     They  arise  from  the 


ABSORPTION.  293 

surface  of  the  mucous  coat,  pass  between  the  serous  and 
muscular  coats,  and  proceed  to  the  small  glands  or  ganglions 
of  the  mesentery.  As  they  emerge  from  these,  they  increase 
rapidly  in  size,  till  they  finally  unite  in  a  large  trunk,  which 
passes  up  along  the  spine,  and  at  last  empties  its  contents 
into  the  left  subclavian  vein  near  the  heart.  Many  physi. 
ologists  are  of  opinion  that  the  lacteals  not  only  terminate 
in  the  thoracic  duct,  but  also  in  numerous  veins  in  the  ab- 
domen. 

5.  The  chyle,  which  is  the  fluid  taken  up  by  the  lacteals, 
does  not  exist  ready  formed  in  the  chyme,  but  is  formed  or 
manufactured  out  of  the  nutrient  principles  contained  in  it, 
by  a  specific  action  of  the  lacteal  vessels  themselves.  In 
like  manner,  the  sap  which  is  contained  in  vegetables,  does 
not  previously  exist  ready  made  in  the  materials  which  are 
absorbed  from  the  ground,  but  is  formed  by  the  peculiar  ac- 
tion of  the  roots.  No  chyle  has  ever  been  found  in  the 
intestines. 

6.  As  the  chyle  passes  on  towards  the  heart,  it  undergoes 
important  changes.  It  loses  some  of  its  albuminous  quali- 
ties ;  while  its  fatty  matter,  its  fibrin,  and  cruor,  considera- 
bly increase.  Its  tendency  to  coagulate,  also  becomes 
greater  as  it  approaches  the  venous  system,  and  it  becomes 
clearer  and  more  transparent.  What  is  the  precise  nature 
of  the  change  which  the  chyle  undergoes  in  passing  through 
the  glands  is  unknown* 

7.  Absorption  not  only  takes  place  from  the  small  intes- 
tines, but  from  the  whole  tract  of  the  intestinal  canal,  inclu- 
ding the  mouth  and  sesophagus.  But  those  vessels  which 
absorb  chyle,  are  chiefly  found  in  the  small  intestines.  ^  It 
is  highly  probable  that  alimentary  substances  may  be  directly 
absorbed  from  the  intestines,  without  undergoing  any  pre- 
vious change  or  assimilation,  like  alcohol  or  water  ;  but  that 
in  their  passage  through  the  absorbent  system,  they  undergo 
a  species  of  digestion,  and  become  in  a  good  degree  fitted 
for  the  replenishment  of  the  blood.     To  this,  however,  alco- 

25* 


294  PHYSIOLOGfY. 

hol  is  an  exception,  as  it  frequently,  if  not  always,  passes 
into  the  blood  unchanged. 

8.  Various  jnedicinal  substances  are  absorbed,  and  enter 
the  circulation,  nearly  or  wholly  unchanged.  Colouring 
matter,  such  as  madder,  is  taken  up  and  carried  into  the 
blood,  and  even  tinges  the  bones.  Oderiferous  particles, 
such  as  of  garlic,  camphor,  asparagus,  &c.,  are  also  readily 
absorbed,  and  in  this  way  the  blood  derives  its  saline  proper- 
ties. It  is  pretty  well  established,  that  articles  not  of  an 
alimentary  nature,  which  are  absorbed,  are  chiefly  taken  up 
by  the  veins,  while  the  lacteals  absorb  chyle  more  readily 
than  any  otiier  substances. 

9.  Absorption  takes  place  from  the  external  surface  or 
skin.  This  is  proved  by  many  facts.  Thirst  may  be 
quenched  by  applying  moist  cloths  to  the  skin,  or  by  bath- 
ing. The  body  increases  in  weight  by  the  use  of  the  bath  5 
and  it  has  been  found  that  the  hand,  immersed  to  the  wrist 
in  warm  water,  will  absorb  from  90  to  100  grains  of  fluid 
in  the  space  of  one  hour.  The  saliva  has  become  bitter  by 
the  absorption  of  sea  water  ;  and  it  is  stated  that  patients 
have  been  supported  by  baths  of  milk  or  broth. 

10.  Medicinal  substances  are  often  absorbed  by  the  skin. 
Mercury,  Spanish  fly,  morphine,  and  many  other  articles  are 
frequently  introduced  into  the  system  through  the  skin. 
Metallic  quicksilver  has  been  found  in  the  bones  of  persons 
who  had  been  subjected  to  mecurial  frictions ;  and  it  has 
also  been  obtained  by  distilling  the  blood  of  rabbits,  dogs, 
and  cats,  which  had  been  rubbed  with  this  mineral.  Gases 
are  also  absorbed  by  the  skin. 

11.  As  every  part  of  the  body  is  subject  to  constant  re- 
novation and  change,  absorption  must  be  continually  going 
on  among  the  particles  and  substance  of  which  each  organ 
is  composed.  This  is  called  interstitial  absorption.  It  is 
this  which  counterbalances  the  action  of  the  nutrient  ves- 
sels, and  preserves  the  form  and  size  of  every  part  of  the 
body.     When  it  is  too  active,  the  body  emaciates  ;  when  it 


ABSORPTION.  295 

is  deficient,  plethora  is  the  result.  In  the  later  periods  of 
life  it  is  more  active  than  nutrition,  and  the  body  dwindles 
in  size  ;  in  youth  the  reverse  is  the  case. 

12.  Foreign  bodies,  introduced  into  the  substance  of  or- 
gans, are  also  absorbed.  Wens  and  tumours  of  considera- 
ble size,  often  disappear  from  the  same  cause.  Instances 
are  known  where  the  absorbent  vessels  have  set  to  work  and 
removed  the  whole  bone  of  a  limb  j  and  but  lately  a  case 
occurred  in  Boston,  in  which  every  particle  of  bone  in  the 
arm  was  thus  taken  up  and  carried  away,  after  a  fracture 
had  occurred.  How  admirable  is  that  arrangement  by 
which  the  vessels  of  absorption  and  secretion  so  act  as  to 
balance  each  other ;  and  how  soon  would  a  loss  of  this 
balance  produce  derangement,  disease,  and  even  death. 

13.  Another  form  of  absorption  is  called  respiratory, 
which  we  have  already  considered  under  the  subject  of  res- 
piration. We  understand  by  it,  merely  the  introduction  of 
oxygen  into  the  blood,  through  the  pulmonary  cells.  Sub- 
stances, however,  in  a  state  of  vapour,  or  fine  dust,  are  also 
readily  imbibed  when  drawn  into  the  lungs ;  such  as  metal- 
lic vapours,  oderiferous  particles,  marsh  and  other  efiluvia. 
It  is  in  this  way,  probably,  that  contagious  diseases  are 
caught. 

14.  It  is  by  means  of  what  physiologists  call  recrementi- 
tial  absorption,  that  fluids  are  removed  from  the  system 
which  are  secreted  upon  surfaces  that  have  no  external  out- 
let ;  as  in  the  cavity  of  the  chest,  abdomen,  brain,  <k;c. 
These  fluids  are  various  :  such  as  the  serous  fluids  ;  the  sy- 
novia of  the  joints  ;  the  fat ;  the  marrow,  and  the  humours 
of  the  eye.  It  is  this  which  prevents  dropsies  in  these  vari- 
ous cavities  ;  and  also  removes  them  when  already  existing. 
This  form  of  absorption  is  also  proved  by  the  fact,  that  fo- 
reign substances,  placed  in  contact  with  these  surfaces,  in  a 
short  time  disappear. 

15.  Another  variety  of  absorption  has  been  called  excre- 
mentiiial ;  as  it  relates  to  the  fluids  which  have  been  excreted. 


296  PHYSIOLOGY. 

These  are  liable  to  be  absorbed ;  at  least  the  more  fluid  parts 
of  them,  by  which  they  are  again  carried  into  the  mass  of 
the  circulating  fluids,  and  such  parts  selected  as  are  fit  for 
the  uses  of  the  animal  economy,  such  is  the  case  with  the 
fluids  exhaled  by  the  skin  ;  the  mucous  membranes ;  the 
saliva  ;  the  bile ;  the  gastric  and  pancreatic  fluids  ;  the  milk, 
&c.  Thus,  has  it  been  remarked,  does  nature  choose  to 
subject  the  materials  of  decomposition  to  a  careful  revision, 
before  rejecting  them  finally  from  the  body. 

16.  All  these  varieties  of  absorption  are  constantly  going 
on  from  the  moment  of  birth  to  that  of  dissolution,  and  all 
the  fluids  which  are  absorbed,  are  changed  in  their  charac- 
ter, and  fitted  to  repair  the  wastes  of  the  system.  Thus, 
by  absorption  in  the  lungs,  oxygen  is  converted  into  one  of 
the  elements  of  the  blood;  in  the  intestines,  chyme  is 
changed  into  chyle ;  in  the  tissues  of  the  organs,  solid  par- 
ticles are  converted  into  fluid  lyjnph ;  and  from  the  cavities 
secreted  and  excreted  fluids  are  again  taken  up  and  thrown 
into  the  circulation,  to  be  once  more  revised  and  elaborated. 

17.  Frogs,  and  several  other  amphibious  animals,  are  fur- 
nished with  large  receptacles  for  the  lymph,  situated  imme- 
diately under  the  skin,  which  exhibit  distinct  and  regular 
pulsations  like  those  of  the  heart.  The  use  of  these  lympha- 
tic  hearts  is  evidently  to  propel  the  lymph  along  the  lympha- 
tic vessels.  The  frog  has  four  of  these  organs ;  the  two 
posterior  being  situated  behind  the  joint  of  the  hip  ;  and  the 
two  anterior  ones  on  each  side  of  the  third  vertebra.  These 
organs  have  also  been  discovered  in  the  toad,  salamander, 
and  lizard. 


Questions. — ^What  is  meant  by  absorption  ?  What  composes  the  ab- 
sorbent  system  ?  Where  do  the  lymphatic  vessels  arise  ?  Describe 
their  structure.  Are  they  found  in  every  part  of  the  body  ?  What  are 
the  agents  of  digestive  absorption  ?  Describe  the  lacteals.  What  is 
chyle  ?  Does  it  exist  ready  formed  in  chyme  ?  What  changes  does 
it  undergo  in  its  passage  to  the  heart  ?    Where  are  the  chyliferous 


ABSORPTION.  297 

vessels  chiefly  found  ?  Are  alimentary  substances  absorbed  without  be- 
ing previously  changed  into  chyle  ?  Is  alcohol  digested  ?  Are  medi- 
cinal substances  absorbed  ?  How  is  this  proved  ?  Does  absorption  take 
place  from  the  skin  ?  What  is  interstitial  absorption  ?  What  is  ema- 
ciation owing  to  ? — plethora  ?  Are  foreign  bodies  absorbed  when  in- 
troduced  into  the  substance  of  organs  ?  Are  the  bones  ever  absorbed  ? 
What  is  respiratory  absorption  '(  What  is  recrementitial  absorption  ? 
What  excrementitial  ?  Are  these  processes  always  going  on  ?  What 
peculiarity  is  there  in  the  lymphatic  system  of  frogs  ? 


CHAPTER  XXIII. 


NUTRITION. 


1.  Nutrition  may  be  considered  as  the  completion  of 
the  functions  of  digestion.  It  is  that  process  by  which  the 
waste  of  the  organs  is  repaired,  and  by  which  their  develop- 
ment and  growth  are  maintained.  Respiration,  digestion, 
circulation,  absorption,  and  secretion,  are  but  separate  links 
in  the  chain  of  nutrition  ;  which  would  be  instantly  de- 
stroyed by  the  absence  of  any  one  of  them. 

2.  In  the  construction  of  a  machine,  or  an  instrument, 
designed  to  last  for  many  years,  the  mechanist  seeks  for  the 
most  durable  materials.  In  making  a  watch,  for  instance, 
he  forms  the  wheels  of  brass,  the  spring  and  barrel-chain  of 
steel,  and  for  the  pivot,  which  is  subject  to  incessant  friction, 
he  employs  the  hardest  of  all  materials — the  diamond.  The 
necessity  for  this  arises  from  the  fact,  that  such  instruments 
do  not  contain,  within  themselves,  the  power  of  repairing 
their  own  losses. 

3.  But  far  different  is  the  case  with  the  animal  machine. 
In  order  to  qualify  it  for  exercising  the  functions  of  life,  it 
must  be  so  constructed  as  to  render  it  capable  of  continual 
alterations,  displacements  and  adjustments ;  and  these  sub- 
ject to  continual  variation,  according  to  the  stage  of  growth, 
and  also  to  the  different  circumstances  in  which  it  may  be 
placed.  Instead,  therefore,  of  a  few  elementary  bodies,  or 
their  simpler  combinations,  nature  has  employed  such  com- 
pounds as  admit  of  greater  change,  and  a  more  variable 
proportion  of  ingredients,  and  greater  diversity  in  the  mode 
of  combination.  It  is  nutrition  that  moulds  these  plastic 
materials,  and  forms  these  ever- changing  compounds  ;  and 
so  preserves  the  animal  machine,  amid  all  the  varying 
changes  of  condition  to  which  it  is  subject. 


NUTRITION.  299 

4.  No  one  can  doubt  that  the  system  is  continually  un- 
dergoing changes.  This  is  proved  by  the  losses  to  which  it 
is  subjected ;  by  the  necessity  of  frequent  supplies  of  ali- 
ment ;  by  the  rapid  wasting  of  flesh  on  the  withdrawal  of 
food  ;  and  by  the  emaciation  caused  by  sickness  and  old  age. 
It  is  also  shewn  by  an  experiment,  which  has  often  been 
made,  viz.  of  giving  madder  to  animals  mixed  with  their 
food ;  which  in  a  short  time  tinges  their  bones  of  a  red, 
colour.  If  the  madder  be  withdrawn,  the  red  colour  in  a  few 
days  disappears  from  the  bones ;  evidently  from  the  effects 
of  absorption. 

5.  Every  part  of  the  body  is  subject  to  this  constant 
change  of  matter.  While  one  set  of  vessels,  the  lympha- 
tics, are  taking  to  pieces  and  carrying  away  the  various 
parts  of  which  the  machine  is  composed,  another  set,  viz., 
the  capillaries,  are  constantly  at  work,  repairing  the  loss, 
depositing  bone,  muscle,  cartilage,  nerve,  tendon,  fat,  mem- 
brane, ligament,  hair,  nails,  &c.  where  each  is  wanted,  and 
this  with  such  regularity  and  order,  as  to  preserve  the  shape, 
size,  and  appearance  of  every  organ,  so  that,  though  after  an 
interval  of  a  few  years  there  may  not  remain  in  the  body  a 
single  particle  of  which,  at  the  former  period,  it  was  made 
up ;  still,  the  individual  preserves  the  same  form  and  features ; 
his  personal  identity  is  never  lost. 

6.  Those  animals,  which  are  the  most  complicated  in 
their  structure,  and  are  distinguished  by  the  greatest  variety 
of  vital  manifestations,  are  subject  to  the  most  rapid  changes 
of  matter.  Such  animals  require  more  frequent,  and  more 
abundant  supplies  of  food,  and  in  proportion  as  they  are  ex- 
posed to  a  greater  number  of  external  impressions,  so  will 
be  the  rapidity  in  this  change  of  matter.  The  frog,  for  in- 
stance, has  been  dug  from  the  earth  many  feet  below  its  sur- 
face ;  and  even  taken  from  cavities  in  solid  limestone,  where 
he  had  been  shut  up  probably  for  centuries,  and  still  exhibit- 
ed signs  of  life  when  exposed  to  the  open  air.  As  he  was  so 
situated  as  to  lose  nothing,  by  secretion  or  evaporation,  of 


300  PHYSIOLOGY. 

course  he  required  nothing  to  supply  any  loss,  but  how  the 
vital  principle  was  preserved  for  such  a  length  of  time,  is  a 
mystery  not  easy  to  be  explained. 

7.  The  blood  contains  all  the  materials  of  nutrition.  The 
process  by  which  the  food  is  changed  into  blood  has  been  al- 
ready explained.  As  it  goes  the  round  of  circulation,  the 
nutrient  capillary  vessels  select  and  secrete  those  parts  which 
are  similar  to  the  nature  of  the  structure,  and  the  other  por- 
tions pass  on  ;  so  that  every  tissue  takes  up  and  converts  to 
its  own  use  the  very  principles  which  it  requires  for  its 
growth ;  or  in  other  words,  as  the  vital  current  approaches 
each  organ,  the  particles  appropriate  to  it,  feel  its  attractive 
force  ;  obey  it ;  quit  the  stream  ;  mingle  with  the  substance 
of  its  tissue,  and  are  changed  into  its  own  true  and  proper 
nature. 

8.  Before  the  body  has  attained  its  full  growth,  the  func- 
tion of  nutrition  is  very  active  ;  a  large  amount  of  food  is 
taken,  being  not  only  sufficient  to  supply  the  place  of  what 
is  lost  by  the  action  of  the  absorbents,  but  also  to  contribute 
to  the  growth  of  the  body.  In  middle  age,  nutrition  and  ab- 
sorption are  more  equal  ;  but  in  old  age  the  absorbents  are 
more  active  than  the  nutrient  vessels  ;  the  size  consequently 
diminishes  ;  the  parts  grow  weaker ;  the  bones  more  brittle  ; 
the  body  bends  forward ;  and  every  function  exhibits  marks 
of  decay  and  dissolution. 

9.  A  few  years  ago,  a  man  by  the  name  of  Calvin  Edson, 
of  Vermont,  commonly  called  the  living  skeleton,  exhibited 
himself  through  the  country  for  money.  From  having  been 
a  large  man,  he  had  wasted  away  by  degrees,  so  that  instead 
of  his  usual  weight,  he  weighed  but  sixty  pounds.  He  had 
been  gradually  losing  flesh  for  eighteen  years  ;  and  he  attri- 
buted it  to  having  taken  cold  from  sleeping  on  the  ground. 
This  emaciation  was  owing  to  the  absorbent  vessels  being 
more  active  than  those  of  nutrition ;  whatever  may  have 
been  the  cause  of  the  loss  of  balance. 


NUTRITION.  301 

10.  On  the  other  hand,  when  the  nutrient  vessels  are  the 
most  active,  the  person  grows  fleshy  and  corpulent,  as  in  the 
case  of  Daniel  Lambert,  who  weighed  seven  hundred  and 
thirty-nine  pounds  at  the  age  of  forty  ;  or  in  that  of  a  Lon- 
don butcher,  who  weighed  eight  hundred  pounds.  There  are 
several  cases  on  record,  where  men  weighed  eight  hundred 
pounds. 

11.  The  degree  of  nutrition,  depends  much  on  the  quanti- 
ty  and  quality  of  the  food.  A  person  who  confines  himself 
chiefly  to  animal  diet,  and  drinks  freely  of  ale  and  other  malt 
liquors,  will  usually  grow  fat ;  but  this  does  not  indicate 
strength  but  weakness.  It  shows  that  there  is  not  only  a 
weakness  of  the  absorbents,  which  are  not  able  to  take  up 
and  remove  the  fat ;  but  also  a  muscular  debility,  and  a  want 
of  force  in  the  circulation.  Motion  is  impeded  ;  the  heart 
is  loaded  and  oppressed ;  the  breathing  is  laborious ;  the 
blood  accumulates  in  the  brain,  and  the  person  is  every  mo- 
ment exposed  to  apoplexy.  In  all  such  cases,  a  sparing  diet 
of  vegetables,  with  proper  exercise,  will  prove  an  effectual 
remedy.  By  sweating,  horse-riding,  and  a  low  diet,  jockeys 
have  not  unfrequently  reduced  themselves  15  or  20  pounds, 
in  a  week  or  ten  days. 

12.  Large  accumulations  of  fat,  it  is  said,  sometimes  take 
place,  as  the  sudden  effect  of  the  influence  of  the  atmosphere. 
Thus,  in  the  short  space  of  twenty-four  hours,  it  is  stated  by 
writers  on  natural  history,  that  a  mist  will  occasionally  fatten 
thrushes,  robins,  &c.,  to  such  a  degree,  than  they  can  hard- 
ly get  out  of  the  way  of  the  sportsman's  gun.  This  however 
is  not  fat,  but  the  appearance  is  owing  to  a  fulness  of  the 
vessels,  from  a  suspension  of  evaporation. 

13.  The  hump  of  the  camel  appears  to  form  a  sort  of  re- 
serve, by  which,  the  Arabs  say,  he  is  nourished,  during  his 
long  journeys.  In  a  period  of  plenty,  the  rapid  secretion  of 
fat  converts  it  into  a  pyramid,  equalling  a  fourth  of  the  ani- 
mal's entire  bulk ;  but  a  journey  through  the  desert  gradual, 
ly  lowers  it,  so  that  it  becomes  scarcely  visible.    The  camel 

26 


303  PHYSIOLOGY. 

then  gives  out,  and  can  travel  no  further  till  the  store  is  re- 
plenished by  rest  and  food.* 

14.  Tumours,  wens,  and  other  morbid  growths  are  the  con- 
sequence of  an  error  in  nutrition.  The  nutritious  vessels  de- 
posite/oi  where  it  is  not  wanted,  and  occasionally  bony  mat- 
ter, where  fibrin  should  be  left  or  something  else.  In  this 
way  only  can  we  account  for  the  bony  concretions  and 
scales  which  are  sometimes  met  with  about  the  heart  and 
blood-vessels  ;  for  the  chalky  deposits  about  the  joints,  in 
cases  of  gout  and  rheumatism,  and  even  for  horny  projec* 
tions,  which  have  in  a  ^qw  cases  been  known  to  sprout  out 
from  the  head.^  A  few  years  ago,  there  were  exhibited  in 
London,  several  individuals  called  the  porcupine  family,  who 
were  all  covered  with  dark  colored  horny  excrescences ;  which 
they  shed  annually  in  the  autumn  or  winter.  These  curious 
organic  peculiarities,  resembled  the  quills  of  the  porcupine, 
and  were  two  or  three  inches  in  length.  But  these  are  only 
exceptions  to  the  usual  regularity  of  nature's  operations,  and 
ought,  instead  of  lessening,  to  increase  our  admiration  at  the 
admirable  symmetry  and  uniformity  that  prevail,  through 
every  department  of  organized  being. 

15.  The  activity  of  muscular  nutrition,  depends  much  on 
exercise.  The  arm  of  a  blacksmith,  or  a  stone-cutter,  for 
instance,  is  generally  large  and  brawny,  because  their  mus- 
cles are  almost  in  constant  use.  The  same  is  true  of  the 
muscles  of  the  leg,  in  rope-dancers  and  tumblers,  also  in 
great  walkers.  Let  any  one  examine  the  muscles  of  the  Ra- 
vel Family,  so  celebrated  for  strength  and  agility  in  all  gym- 
nastic exercises,  and  he  will  find  them  not  only  unusually  de- 
veloped,, but  also  hard  and  firm.  If  a  person  meet  with  an 
accident  so  that  he  is  unable  to  walk,  although  his  appetite 
remains,  his  muscles  dwindle  away  for  want  of  exercise.  If 
then,  a  person  who  leads  a  sedentary  life  be  corpulent,  the 
excess  is  not  to  be  considered  sound  muscle  or  flesh,  but  fat, 
which,  I  have  before  stated,  is  a  sign  of  weakness. 


*  Burkhardt's  travels. 


NUTRITION.  303 

Questions. — Wliat  is  nutrition  ?  What  is  sought  for  in  constructing 
a  machine  ?  Why  the  necessity  for  this  ?  How  is  it  in  the  animal 
machine  ?  Is  the  system  constantly  undergoing  changes  ?  How  is 
this  shown  ?  What  vessels  repair  the  losses  of  the  system  ?  What  ani- 
mals are  subject  to  the  most  rapid  changes  of  matter  ?  What  contains 
the  materials  of  nutrition  ?  When  is  nutrition  most  active  ? — when 
Jeast  so  ?  What  is  the  consequence  ?  What  does  the  degree  of  nutri- 
tion depend  on  ?  Does  fatness  indicate  strength  ?  Why  not  ?  What 
use  does  the  hump  of  the  camel  serve  ?  What  are  tumours  and  wens 
■owing  to  ?     What  causes  muscular  nutrition  ? 


CHAPTER  XXIV. 


ANIMAL    HEAT. 


1.  Calorification,  is  a  function  of  animal  bodies,  not  yet 
thoroughly  understood.  We  see  certain  phenomena,  but  the 
causes  are  hidden  from  our  view.  It  is  very  doubtful  wheth- 
er we  shall  ever  be  able  to  penetrate  the  veil  which  con- 
ceals the  wonderful  operations  of  vital  chemistry  ;  and  per- 
haps it  would  lead  to  no  useful  result  if  we  could  ;  should 
we  ever  attain  to  the  knowledge  of  all  the  natural  laws  of 
life,  we  shall  then  be  assured  that  it  is  only  in  consequence 
of  their  violation  that  man  pays,  by  suffering,  sickness  and 
premature  death,  the  penalty  of  their  transgression. 

2.  What  causes  the  temperature  of  the  body  to  be  main- 
tained at  an  average  of  ninety-eight  degrees,  and  this,  too, 
under  all  climates,  and  at  all  seasons  ?  In  the  first  place, 
respiration  is  much  concerned  in  the  production  of  animal 
heat.  It  was  once  indeed  believed,  that  the  chief  office  of 
respiration  was  to  cool  the  blood ;  and  that  the  heart  was  the 
great  furnace  of  the  system,  where  all  the  heat  was  pro- 
duced. 

3.  When  it  was  discovered  that  both  in  combustion  and 
respiration,  carbonic  acid  was  produced,  and  oxygen  ab- 
sorbed, it  was  at  once  surmised,  that  breathing  must  be  a  kind 
of  combustion  by  which  all  the  heat  of  the  body  is  generat- 
ed. But  it  was  objected  to  this,  that  if  the  heat  was  all  pro- 
duced in  the  lungs,  why  were  not  the  lungs  hotter  than  the 
other  parts  of  the  body,  as  those  parts  of  a  stove  in  contact 
with  the  fuel,  are  hotter  than  those  at  a  distance. 

4.  This  objection  to  Mr.  Black's  hypothesis,  led  Mr. 
Crawford  to  propose  the  following  solution.  Although  ani- 
mal heat  is  produced  in  the  lungs  by  the  process  of  respira- 
tion, yet  as  arterial  blood  has  a  greater  capacity  for  calorie 


ANIMAL    HEAT.  3Q5 

than  menotis,  that  is,  requires  more  caloric  to  preserve  it  at 
the  same  temperature,  the  heat  becomes  latent  in  saturating 
this  increased  capacity  of  arterial  blood  ;  and  is  gradually 
given  off  in  every  part  of  the  body,  as  the  blood  assumes  the 
venous  character.  But  unfortunately  for  this  theory,  it  has 
been  ascertained  that  there  is  no  difference,  and  that  arterial 
and  venous  blood  have  an  equal  capacity  for  heat, 

5.  But  however  it  may  be  explained,  no  one  can  doubt, 
that  calorification  is  closely  connected  with  respiration.  If 
the  latter  is  increased  by  any  cause,  the  heat  of  the  body  is 
also  increased.  When  it  is  impeded,  as  in  asthma,  fainting, 
breathing  deleterious  gases,  and  suffocation,  the  animal  heat 
is  sensibly  diminished.  Those  animals  whose  respiratory  ap- 
paratus is  the  most  perfect  and  the  best  developed,  have  the 
highest  temperature,  as  we  see  in  birds,  whose  bodies  are  sev- 
eral degrees  warmer  than  the  human  species. 

6.  On  the  contrary,  if  we  look  at  the  cold-blooded  ani- 
mals, we  shall  find  that  a  large  proportion  of  them  live  in 
water,  where  the  supply  of  oxygen  is  but  scanty,  and  that 
their  respiration  is  very  imperfect ;  while  in  animals  that 
lie  torpid  during  the  winter,  and  are  quite  cold,  resptration 
is  almost  if  not  quite  suspended.  According  to  Majendi«j 
respiration  produces  four-fifths  of  the  heat  in  herbivorous 
-animals ;  three-fourths  in  carniverous,  and  the  same  in 
birds. 

7.  It  is  found  by  experiment,  that  arterial  blood  is  warmer 
than  venous.  The  blood  is  found  to  acquire  one  degree  of 
heat  in  passing  through  the  lungs,  and  as  the  whole  mass 
of  the  blood  passes  through  the  lungs  twenty  times  an  hour, 
it  follows,  that  the  system  receives  from  respiration  twenty 
degrees  of  heat  in  an  hour,  or  two  hundred  and  forty  degrees 
-every  twelve  hours.  Respiration,  then,  is  one  of  the  chief 
sources  of  animal  heat. 

8.  Another  theory  in  relation  to  animal  heat  is,  that  it  is 
|)roduced  by,  or  depends  on,  nervous  influence.      This  is 

26* 


30^  PHYSIOLOGY. 

supported  by  a  few  experiments  of  Mr.  Brodie,  who  kept  up 
artificial  respiration  in  animals  after  cutting  off  their  heads. 
He  found  that,  notwithstanding,  the  usual  changes  took 
place  in  the  blood,  and  in  the  air  introduced  into  the  lungs, 
yet  the  temperature  fell  even  faster  than  in  another  animal 
killed  at  the  same  time,  in  which  respiration  was  not  kept 
up.  This  experiment,  however,  is  not  conclusive,  as  an  ani- 
mal may  be  cooled  by  forcing  too  much  air  into  the  lungs ; 
and  if  less  be  introduced  the  heat  may  be  preserved  for  some 
time. 

9.  Another  theory  is,  that  animal  heat  is  generated  in 
the  capillary  system.  This  is  supported  by  the  fact,  that 
some  parts  of  the  body  are  often  hotter  than  others,  as  in 
inflammation  ;  that  it  is  always  proportioned  to  the  ener- 
getic action  of  any  organ,  as  the  head  becomes  hotter  by 
hard  study  ;  and  a  glass  of  spirits  excites  a  feeling  of  warmth 
in  the  stomach. 

10.  It  may  be  laid  down  as  an  axiom,  or  admitted  truth,^ 
that  all  movements  among  the  particles  of  bodies  which 
cause  a  change  of  state,  are  attended  with  change  of  tem- 
perature. This  is  tlie  case  in  combustion,  which  is  a 
union  of  oxygen  with  the  inflammable  body,  and  the 
production  of  carbonic  acid  ;  and  so  also  when  two  liquids 
are  mixed  together,  which  chemically  unite,  heat  is  always 
evolved.  Now,  in  all  the  processes  of  nutrition,  secretion, 
digestion,  respiration,  &c.,  such  changes  are  constantly 
going  on.  In  respiration,  a  part  of  the  blood  is  thrown  oflT 
in  a  gaseous  form,  while  a  quantity  of  oxygen  unites  with 
the  remaining  portion.  This  process,  according  to  all  the 
known  laws  of  caloric,  must  be  attended  with  an  elevation 
of  temperature.     And  this  proves  to  be  the  fact. 

11.  By  the  function  of  nutrition,  fluids  are  changed  into 
solids  ;  and  by  absorption,  solids  are  changed  into  fluids  ;  by 
secretion,  new  chemical  compounds  are  formed  out  of  a  {ew 
simple  elements  contained  in  the  blood ;  and  by  digestion,  a 


ANIMAL    HEAT.  307 

new  fluid,  chyle,  is  formed  out  of  the  solids,  which  constitute 
the  food.  By  all  these  processes,  animal  heat  must  necessa- 
rily be  generated. 

12.  But  in  order  to  the  production  of  animal  heat,  by  the 
action  of  the  capillary  vessels,  two  conditions  are  necessary. 
One  is,  the  presence  of  arterial  blood ;  the  other,  the  action 
of  the  nervous  system.  That  arterial  blood  is  necessary,  is 
shown  by  the  operation  of  tying  the  vessels  which  supply  a 
limb  with  blood.  The  consequence  always  is,  that  the  tem- 
perature immediately  falls,  and  such  limbs  have  to  be  wrap- 
ped in  cotton,  and  other  means  used  to  preserve  a  comforta- 
ble degree  of  warmth.  That  nervous  influence  is  also 
productive  of  animal  heat,  is  shown  by  dividing,  in  like 
manner,  the  nerves  which  go  to  any  part.  The  temperature 
of  a  paralytic  limb  is  always  lower  than  that  of  the  sound 
one. 

13.  It  may  be  concluded  then,  that  respiration,  circula- 
tion, and  nervous  influence,  all  co-operate  in  producing 
animal  heat,  or  that  they  are  conditions  essential  to  this 
phenomenon.  We  here  also  perceive  a  circle  of  actions  ; 
or  a  chain,  composed  of  many  links,  no  one  of  which  can 
be  spared.  Each  one  contributes  to  a  result  essential  to 
organic  existence,  and  one  of  the  most  curious  and  wonder- 
ful which  the  mind  can  contemplate. 

14.  If  these  principles  be  correct,  we  should  expect  to 
find  the  greatest  heat  in  those  animals  whose  structure  is 
the  most  complex ;  whose  organic  or  vital  actions  are  the 
most  intense ;  and  whose  changes  are  the  most  rapid.  Now 
all  these  conditions  belong  to  the  warm-blooded  animals  es- 
pecially, and  particularly  to  birds,  whose  temperature 
exceeds,  by  several  degrees,  that  of  man.  In  them,  as  I 
have  already  stated,  respiration  is  more  perfect,  and  the  cir- 
culation more  rapid. 

15.  Upon  the  same  principles,  it  would  also  follow,  that 
animal  heat  would  be  the  highest  in  those  portions  of  the 
body  where  the  organic  actions  are  most  active.     And  such 


308  PHYSIOLOGY. 

is  actually  ihe  case.  If  a  thermometer  be  placed  over  the 
xjhest,  the  stomach,  or  the  liver,  it  will  indicate  a  higher 
temperature  by  some  degrees  than  exists  in  the  extremities, 
because  it  is  near  the  seat  of  respiration,  digestion,  and  the 
largest  secretory  organ  in  the  body.  The  temperature  of 
different  parts  of  the  animal  body  ranges  from  91  to  100 
degrees  ;  and  in  fever  to  112,  which  is  marked  "fever  heat" 
on  the  thermometer. 

16.  Those  animals  that  belong  to  the  class  mammalia, 
and  which  live  in  water,  such  as  the  whale,  the  dolphin,  and 
the  porpoise,  have  a  temperature  as  high  as  that  of  man. 
Captain  Scoresby  found  the  temperature  of  a  whale,  in  the 
Arctic  Ocean,  to  be  104  degrees ;  while  that  of  the  polar 
bear  and  wolf  were  no  greater.  Warm-blooded  animals  are 
generally  covered  with  hair  or  feathers,  to  protect  them 
from  the  cold ;  cold-blooded  animals  need  no  protection,  as 
they  can  live  in  a  temperature  as  low  as  the  freezing  point 
of  water.  Seals,  bears  and  walruses  in  the  Northern  Ocean, 
are  protected  by  a  coating  of  hair  ;  the  whale  is  protected 
by  the  great  thickness  of  its  skin  and  the  stratum  of  fat  im- 
mediately beneath  it.  Dr.  Edwards  states  that  frogs,  which 
can  live  in  water  at  32  degrees,  will  die  in  a  short  time  in 
water  at  105  degrees. 

17.  But  this  does  not  seem  to  be  the  case  in  all  cold- 
blooded animals.  In  some  of  the  warm  springs  in  Brazil, 
which  have  a  temperature  of  88,  many  small  fishes  are 
found ;  and  also  in  a  hot  spring  at  the  Manillas,  which 
raises  the  thermometer  to  158  degrees;  and  Humboldt,  in 
his  travels,  tells  us  that  in  the  province  of  Quito,  in  South 
America,  he  saw  fishes  thrown  up  from  the  bottom  of  a  vol- 
cano, along  with  water  and  heated  vapour,  which  raised  the 
thermometer  to  210,  or  only  two  degrees  short  of  the  boiling 
point.  Lord  Bute  saw  beetles  in  the  boiling  springs  of  Al- 
bano,  which  died  when  plunged  into  cold  water ;  and  Dr. 
EUiotson  states  that  a  gentleman  of  his  acquaintance  boiled 
some  honeycomb  two  years  old,  and  after  extracting  all  the 


ANIMAL    HEAT.  309 

honey,  threw  the  refuse  into  a  stable,  which  was  soon  filled 
with  bees. 

18.  Warm-blooded  animals  have  the  faculty  of  preserv. 
ing  the  same  degree  of  heat  in  nearly  every  variety  of  cli- 
mate. During  Captain  Parry^s  voyage  to  the  Arctic  seas, 
in  quest  of  the  northwest  passage,  the  crews  of  his  vessels 
were  often  exposed  to  a  temperature  of  fifty  degrees  below 
zero,  or  one  hundred  and  fifty  degrees  below  that  of  their 
own  bodies,  and  still  they  were  able  to  resist  it,  and  escape 
being  frost  bitten.  When  the  temperature  was  thirty-two 
degrees  below  zero,  they  found  that  of  an  Arctic  fox  one 
hundred  and  six  degrees,  which  shows  what  a  strong  coun- 
teracting energy  there  is  in  animals,  against  the  effects  of 
cold. 

19.  The  human  body  can  also  resist  great  heat  as  well  as 
cold.  In  summer  we  are  often  exposed,  when  in  the  sun,  to 
a  temperature  many  degrees  above  that  of  the  body,  but  the 
heat  of  the  body  is  not  elevated.  Chantry,  the  sculptor, 
often  entered  his  furnace  when  heated  for  drying  his  moulds, 
when  the  thermometer  in  it  stood  at  three  hundred  and 
twenty ;  and  his  workmen  did  the  same  when  the  tempera- 
ture was  three  hundred  and  forty  degrees.  Dunglison 
states  that  Chabert  entered  an  oven  with  impunity,  the 
heat  of  which  was  from  four  hundred  to  six  hundred  de- 
grees. In  all  these  cases,  where  even  water  was  boiled,  and 
meat  cooked  to  a  crisp,  the  heat  of  the  body  was  raised  but 
a  few  degrees. 

20.  In  these  cases  the  heat  of  the  body  is  kept  down  to 
near  the  natural  standard,  by  exhalation,  or  sweating.  This 
carries  off"  the  heat  in  a  state  of  vapour  as  fast  as  it  is  pro- 
duced. For  the  same  reason,  water  cannot  be  heated  above 
two  hundred  and  twelve  degrees,  as  it  then  escapes  in  the 
form  of  vapour.  By  evaporation,  also,  bottles  of  wine  are 
cooled  in  summer,  by  wrapping  them  round  with  wet 
cloths.  In  India,  it  is  said,  that  ice  is  produced  in  a  simi- 
lar manner.     If  an  animal  be  saturated  with  moisture,  and 


310  PHYSIOLOGY. 

placed  in  a  hot  oven,  it  soon  dies,  because  the  exhalation 
from  the  body  is  prevented.  It  is  for  this  reason,  also,  that 
we  feel  the  heat  more  in  damp  weather  than  in  dry,  although 
the  temperature  be  lower.  Such  weather  is  called  sultry, 
close,  muggy,  6^c,,  because  the  saturation  of  the  air  by 
moisture,  prevents  the  escape  of  heat  by  evaporation  from 
our  bodies. 

21.  In  infancy,  the  faculty  of  generating  animal  heat  is 
much  less  than  in  adult  age.  This  is  the  chief  cause  why 
so  many  perish  during  the  first  years  of  Hfe,  and  particular- 
ly in  winter,  during  the  first  few  days.  At  this  period,  the 
temperature  of  infants  is  only  about  ninety-three  degrees, 
and  in  some  instances  not  more  than  eighty,  and  is  rapidly 
diminished  by  slight  exposures.  This  shows  the  great  im- 
portance of  guarding  against  the  effect  of  cold,  by  proper 
clothing,  and  a  regulated  temperature  of  houses.  Man 
has  no  natural  protection  against  the  influence  of  cold,  but 
reason  was  given  him  as  a  substitute.  How  kw  appear 
to  employ  this  faculty,  in  guarding  against  atmospheric 
vicissitudes  by  a  proper  adaptation  of  the  dress ;  and  in 
consequence,  how  many,  instead  of  consulting  their  health, 
-comfort,  and  usefulness,  fall  victims  to  neg;ligence  or  fashion '! 


Questions. — What  is  calorification  ?  What  are  the  causes  of  animal 
heat  ?  Why  was  it  surmised  that  respiration  was  concerned  in  this 
process  ?  What  objections  to  this  ?  What  was  Crawford's  hypothesis  ? 
What  occurs  when  respiration  is  impeded  ?  What  occurs  in  cold- 
blooded animals  ?  How  much  heat,  according  to  Magendie,  is  produced 
by  respiration  in  herbiverous  animals  ? — in  carniverous  ? — in  birds  ? 
Is  arterial  blood  warmer  than  venous  ?  How  much  heat  does  the  blood 
acquire  in  passing  through  the  lungs  ?  How  many  degrees  does  the 
system  acquire  from  this  source  in  24  hours  ?  What  is  Brodie's  theory 
with  respect  to  animal  heat  ?  What  facts  in  favour  of  it  ?  What  is 
said  of  animal  heat  being  generated  in  the  capillary  system  ?  What 
axiom  in  relation  to  a  change  in  the  particles  of  bodies  has  a  bearing 
on  this  subject  ?  What  conditions  are  necessary  to  the  production  of 
animal  heat  by  the  action  of  the  capillaries  ?     How  is  this  proved  ? 


ANIMAL    HEAT.  311 

What  functions  co-operate  in  the  production  of  animal  heat  ?  In  what 
animals  is  heat  the  greatest  ?  Why  ?  In  what  parts  of  the  body  is  it 
the  highest  ?  Why  ?  What  is  the  temperature  of  the  mammaha  that 
live  in  water  ?  What  effect  does  a  change  of  temperature  have  on 
cold-blooded  animals  ?  Can  warm-blooded  animals  preserve  the  same 
temperature  in  every  climate  ?  How  is  this  effected  ?  What  effect 
will  checking  evaporation  have  ?  Is  the  faculty  of  generating  h^eat 
less  in  infancy  ?    What  inference  do  we  draw  from  this  fact  ? 


CHAPTER  XXV. 

THE    VOICE. 

1.  The  voice  is  a  sound  produced  in  the  larynx,  or  wind- 
pipe, by  the  passage  of  air,  either  to  or  from  the  lungs.  It 
is  generally  caused  in  the  act  of  respiration,  and  its  seat  is 
the  larynx,  which  forms  the  very  top  of  the  wind-pipe,  and 
externally  makes  that  prominence  at  the  fore-part  of  the 
neck,  called  Adam's  apple.  It  is  connected  above  with  the 
bone  of  the  throat,  by  means  of  small  muscles,  and  behind 
with  the  esophagus,  or  passage  to  the  stomach. 
[  2.  The  larynx  is  composed  of  four  cartilages,  closely  con- 
nected by  membranes  ;  these  are  .called  the  thyroid,  the  cri- 
coid, and  the  two  arytenoid  cartilages.  The  thyroid  cartilage 
is  shaped  somewhat  like  a  shield,  and  hence  its  name.  It 
forms  the  front  and  lateral  part  of  the  larynx,  being  broader 
in  front  than  behind,  and  made  up  of  two  parts  which  join 
in  the  front  of  the  neck  at  an  acute  angle,  thus  making  the 
prominence  spoken  of  above.  It  has  two  projections  above, 
and  two  below ;  the  former  connect  it  with  the  bone  of  the 
tongue,  and  are  called  the  upper  horns ;  by  the  latter  which 
are  called  the  lower  horns,  it  is  united  with  the  cricoid  carti- 
lELge,  by  means  of  ligaments. 

3.  The  cricoid  cartilage  is  so  called  from  its  resemblance 
to  a  ring.  It  lies  immediately  below  the  thyroid  cartilage, 
being  broad  at  its  sides,  narrow  in  front,  and  connected  with 
the  thyroid  cartilage  behind  by  a  still  broader  surface.  In 
front  it  is  not  connected  with  the  thyroid  cartilage ;  but  the 
space  is  occupied  by  the  lining  membrane  of  the  larynx, 
covered  with  the  common  integuments. 

4.  The  arytenoid  cartilages  are  much  smaller  than  the  oth- 
ers, and  are  situated  at  the  back  part  of  the  larynx,  in  con- 
nection  with  the  cricoid  cartilage.     They  have  small  mus- 


TIIE    VOICE.  313 

cles  attached  to  them,  by  which  they  are  moved  sideways, 
and  it  is  by  these  motions  that  the  opening  in  the  larynx, 
called  the  glottis,  is  enlarged  or  contracted.  Two  fibrous 
ligaments  connect  these  cartilages  with  the  thyroid  ;  these 
two  are  called  vocal  chords,  as  they  are  supposed  to  be 
particularly  concerned  in  the  production  of  voice.  They 
pass  from  the  artenoid  cartilages  to  the  angle  formed  by  the 
two  side  pieces  of  the  thyroid,  and  are  about  half  an  inch  in 
length.  The  opening  between  them  is  called  glottis,  rima- 
glottidis,  or  chink  of  the  glottis. 

5.  The  epiglottis  is  the  little  moveable  cartilage  ;  which 
lies  over  the  top  of  the  wind-pipe,  at  the  root  of  the  tongue, 
and  has  been  compared  to  a  trap-door.  It  prevents  the  food 
from  passing  into  the  wind-pipe  when  we  swallow.  From 
its  elasticity,  its  position  is  usually  perpendicular,  except  in 
the  very  act  of  swallowing,  when  the  tongue  is  carried  back- 
wards, so  as  to  bring  it  exactly  over  the  opening  ;  this  pre- 
vents the  passage  of  foreign  bodies  into  the  lungs. 

6.  The  larynx  is  abundantly  supplied  with  nerves  which 
are  given  off  from  the  eighth  pair.  The  thyroid  gland  is  a 
body  consisting  of  two  lobes,  lying  one  on  each  side,  and 
somewhat  below  the  larynx  ;  the  use  of  which  is  unknown ; 
it  is  the  seat  of  the  disease  called  goitre,  or  swelled  neck,  so 
common  in  Switzerland,  and  some  other  countries. 

7.  Such  is  the  description  of  the  organs  immediately  con- 
cerned in  the  voice  ;  the  whole  vocal  apparatus,  however, 
comprises  the  muscles  concerned  in  breathing,  the  mouth, 
and  nasal  cavities,  as  well  as  the  parts  above  mentioned.  It 
is  essential  to  the  production  of  voice  that  the  air  should 
pass  from  the  lungs  through  the  larynx  ;  for  if  an  opening 
be  made  in  the  wind-pipe,  so  that  the  air  escapes,  the  voice 
is  lost.  I  lately  witnessed  this  in  a  man  who  undertook  to 
destroy  his  life  by  cutting  his  throat.  He  succeeded  in  cut- 
ting the  wind- pipe  completely  off,  but  as  no  large  blood  ves- 
sels were  divided,  he  got  well.     This  man  could  not  utter  a 

27 


314  PHYSIOLOGY. 

syllable,  not  even  in  a  whisper,  until  the  wind-pipe  healed 
up  ;  his  voice  was  then  restored  to  its  former  condition. 

8.  Volition  is  necessary  to  the  production  of  voice.  If 
the  nerves  going  to  the  larynx  are  cut,  the  voice  will  be 
lost.  Palsy  of  the  muscles  of  the  larynx,  also  causes  dumb- 
ness ;  and  fear  effects  the  voice  by  paralyzing  muscular  ef- 
fort. The  epiglottis  is  found  not  to  be  concerned  in  the  pro- 
duction of  the  voice,  as  it  may  be  removed  without  affecting 
it ;  its  sole  office  being  to  guard  the  wind-pipe  against  the  in- 
troduction of  foreign  substances. 

9.  It  has  been  proved  by  experiments,  that  nearly  all  the 
larynx  except  the  chordm  vocales,  or  vocal  chords,  may  be 
removed  without  destroying  the  voice.  These  are  the  small 
ligaments  that  pass  from  the  arytenoid  cartilages  to  the  thy- 
roid cartilages,  and  are  usually  called  the  inferior  ligaments^ 
or  the  lower  vocal  chords. 

10.  It  is  now  ascertained  that  these  chords  perform  the 
principal  part  in  the  production  of  the  voice.  In  what  way 
this  is  done,  is  not  precisely  known ;  but,  we  may  suppose 
that  the  air  in  passing  from  the  lungs  in  expiration,  is  forced 
out  of  small  cavities,  as  the  air-cells  and  minute  branches  of 
the  wind-pipe,  into  the  main  channel ;  it  it  is  thence  sent 
through  a  narrow  passage,  on  each  side  of  which  is  a  vibra- 
tory chord  ;  the  vibrations  of  which,  by  the  action  of  the  air 
produces  voice  or  sound. 

11.  It  has  been  said  that  if  this  theory  of  the  voice  be  cor- 
rect, there  ought  to  be  sound  produced  by  forcing  air  through 
the  wind-pipe  of  a  dead  animal.  But  this  takes  for  granted 
what  is  not  true,  namely,  that  the  voice  is  the  result  of  a 
purely  mechanical  process  ;  instead  of  which,  it  is  a  vital 
function,  performed  by  living  agents,  and  therefore  under 
the  control  of  voluntary  action. 

12.  In  producing  sound,  there  can  be  no  doubt  that  nume- 
rous voluntary  muscles  are  put  in  action,  bringing  the  ary- 
tenoid cartilages  in  contact  with  each  other,  thus  putting 
upon  the  stretch  the  lower  vocal  chords  which  are  attached 


THE    VOICE.  315 

-to  them.  It  is  therefore  by  no  means  strange  that  vocal 
sound  cannot  be  made  by  forcing  air  through  the  larynx  of 
a  dead  animal. 

13.  It  has  often  been  disputed  whether  the  larynx  was  a 
wind  or  stringed  instrument.  Most  physiologists  at  the  pre- 
sent time,  regard  it  as  a  wind  instrument  of  the  reed  kind, 
such  as  the  clarionet,  hautboy,  &;c.,  and  they  differ  chiefly 
in  explaining  the  various  modifications  of  the  tone  and  qua- 
lity of  the  voice.  There  is,  however,  great  reason  to  believe 
that  it  partakes  of  the  character  of  both. 

14.  The  strength  of  the  voice  depends  on  the  extent  of  the 
vibrations,  of  course  on  the  size  of  the  larynx,  and  partly 
^Iso  on  the  forcT;  with  which  the  air  is  sent  from  the  lungs. 
Thus  the  voice  of  men  is  much  stronger  than  that  of  wo- 
men and  children  ;  and  that  of  a  well  person  stronger  than 
that  of  a  feeble  individual.  The  change  of  voice  at  the  pe- 
riod of  manhood,  is  owing  to  the  increase  in  size  of  the  la- 
rynx. 

15.  The  tone  of  the  voice  can  be  almost  infinitely  varied  : 
indeed,  nothing  can  exceed  the  human  organ  of  voice  in  va- 
riety and  execution.  We  may  perhaps  safely  calculate  the 
number  of  changes  that  can  be  produced  ill  the  organ,  at 
least  to  be  equal  to  the  number  of  muscles  employed,  togeth- 
er with  all  the  combinations  of  which  they  are  capable. 
Now,  the  muscles  immediately  concerned  in  the  function  of 
voice  are  seven  pair.  Besides  these,  however,  there  are  ff- 
teen  other  pair,  which  are  connected  with  the  larynx,  and 
have  more  or  less  to  do  in  regulating  the  motions  of  the  car- 
tilages, keeping  them  steady  or  moving  them  in  different  di- 
rections. 

16.  Now,  if  there  were  only  seven  pair  of  muscles  con- 
cerned, the  different  movements  which  their  varied  action 
would  produce,  will  amount  to  more  than  sixteen  thousand. 
Taking  the  whole  number  of  muscles  into  account,  the  dif- 
ferent combinations  will  be  more  than  one  thousand  million, 
But  besides  these;,  there  are  the  midriffs  or  diaphragm,  the  ah. 


SI  6  PHYSIOLOGY. 

dominal,  and  the  intercostal  muscles,  all  of  which  are  con* 
cerned  in  the  production  of  voice  !  "  How  wonderful  is 
man !     How  passing  wonder,  He  that  made  him  such  !" 

17.  The  precise  manner  in  which  such  an  infinite  varie- 
ty of  tones  is  produced,  is  unknown  ;  physiologists  explain- 
ing the  matter  according  to  their  respective  theories,  wheth- 
er the  larynx  be  a  wind  or  stringed  instrument.  The 
glottis  doubtless  contracts  for  the  production  of  acute  or 
sharp  tones  ;  but  how  grave  ones  are  produced,  admits  of 
doubt,  whether  it  be  owing  to  a  lengthening  of  the  trachea, 
or  the  relaxation  of  the  vocal  chords.  Perhaps  it  would  be 
near  the  truth  to  say,  that  both  these  circumstances  take 
place,  but  that  the  grave  notes  are  chiefly  caused  by  the 
latter. 

18.  Ventriloquism  consists  in  making  the  voice  appear  to 
proceed  from  other  persons  in  various  places,  either  in  or  out 
of  the  room.  To  do  this  with  success  the  performer  first  di- 
rects the  attention  of  the  audience  to  the  place  from  whence 
he  wishes  to  have  his  voice  appear  to  proceed ;  he  then 
changes  his  voice  in  such  a  manner  as  makes  it  sound  like 
that  of  another  person,  or  the  noise  of  the  animal  he  designs 
to  imitate,  and  in  doing  so,  avoids  all  the  words  which  have 
labials,  or  which  require  the  use  of  the  lips.  This  modifica- 
tion of  voice  is  supposed  to  be  performed  by  the  muscles  of 
the  larynx,^  and  this  is  known  to  be  the  sole  organ  of  all  the 
natural  cries. 

19.  There  are  generally  considered  to  be  two  kinds  oi 
voice,  the  natural  and  acquired.  The  former  is  possessed  in 
common  with  man,  by  the  inferior  animals,  but  the  latter  iS: 
enjoyed  by  man  alone  to  any  extent.  The  natural  voice 
consists  in  mere  cries,  and  is  possessed  by  the  infant  as 
soon  as  it  is  born,  and  also  by  idiots,  and  by  those  who 
are  born  dumb.  It  is  seated  entirely  in  the  larynx,  and 
does  not  depend  on  intellect,  or  hearing. 

20.  The  acquired  voice,  on  the  contrary,  is  the  result  of 
imitation,  and  enables  us  to  express  our  ideas  in  words  or 


THE    VOICE.  317 

articulate  sounds.  In  this  way  the  child  learns  to  imitate 
the  sounds  which  he  hears,  and  if  he  is  deaf,  of  course  he 
will  never  learn  to  speak  :  children  therefore  are  dumb^ 
because  they  are  deaf.  Idiots  also  are  dumb,  although  they 
can  hear ;  intellectual  faculties,  therefore,  are  necessary  to 
speech  as  well  as  hearing ;  and  it  is  probably  owing  to  a 
want  of  intellect  that  infants  do  not  speak  at  an  earlier 
age.  For  the  same  reason,  the  ourang  outang  cannot  ac- 
quire the  faculty  of  speech.  In  the  acquired  voice,  the 
tongue  and  lips  are  brought  into  exercise,  but  neither  ef 
them  can  be  regarded  as  absolutely  essential  to  the  faculty 
of  speech. 

.  21.  Whistling  is  caused  by  the  expired  air  being  broken 
or  divided  by  the  lips,  which  act  the  part  of  the  glottis  in 
the  production  of  the  voice.  Whispering  consists  in  the 
articulation  of  the  air  of  expiration,  and  is  wholly  per- 
formed in  the  vocal  tube  ;  hence  the  impossibility  of  sing- 
ing in  a  whisper — singing  being  produced  in  the  glottis* 
Sighing  is  produced  by  the  rushing  of  the  air  along  the  air 
passages ;  and  the  voice  is  also  concerned  in  laughing,  cry.- 
ing,  coughing,  sneezing,  yawning,  and  sobbing,  modified  by 
the  mode  of  respiration. 

22.  Singing  is  a  very  useful  art,  and  ought  to  be  learned 
by  every  person.  It  not  only  contributes  to  our  intellectual 
gratification,  but  is  also  of  essential  benefit  to  the  bodily 
:Iiealth.  For  these  reasons,  and  because  it  conduces  to  be- 
get an  habitual  cheerfulness  of  mind,  it  ought  to  be  taught 
in  all  schools  and  academies,  and  made  a  part  of  the  daily 
exercises,  as  it  is  in  Germany,  and  in  our  own  infant 
schools. 


Questions.  — ^What  is  voice  ?  Where  is  its  seat  ?  What  is  the  la- 
;rynx  composed  of  ?  What  is  the  shape  of  the  thyroid  cartilage  ?  De- 
scribe its  structure  ?  The  cricoid  ? — its  structure  and  situation  ?  De- 
scribe the  arytenoid  cartilages  ?  What  is  the  glottis  ? — the  epiglottis  ? 
What  is  the  thyroid  gland? — its  use? — the  seat  of  what  disease? 

23'* 


31;S  PHYSIOLOGY. 

What  does  the  whole  vocal  apparatus  comprise  ?  What  is  essentiai 
to  the  production  of  voice  ?  What  effect  has  cutting  the  nerves  which 
go  to  the  larynx  ?  What  part  of  the  larynx  can  be  removed  without 
efiecting  the  voice  ?  What  are  chiefly  concerned  in  the  production  of 
voice  ?  Is  the  larynx  a  wind  or  stringed  instrument  ?  What  does  the 
strength  of  the  voice  depend  on  ?  What  is  a  change  of  voice  owing 
to  ?  What  is  said  of  the  tone  of  the  voice  ?  How  many  muscles  are  con- 
eemed  ?  How  many  combinations  can  they  produce  ?  How  are  acute 
sounds  produced  ?  How  grave  ones  ?  What  is  ventriloquism  ?  What 
ja  natural  voice  ?  What  acquired  ?  Why  are  deaf  children  dumb  ? 
Why  are  idiots  ?  What  is  whistling  ? — ^whispering  ? — sighing,  &c.? 
What  is  said  of  singing  ? 


CHAPTER  XXVL 

LOCOMOTION   AND    ITS    ORGANS. 

1.  Man  is  distinguished  from  the  vegetable  world,  not 
only  by  his  possessing  a  nervous  system,  organs  of  sense, 
and  voice,  but  also  by  the  power  of  locomotion,  or  moving 
from  place  to  place.  This  power  connects  him  with  the 
external  world,  enlarges  his  sphere  of  action  and  increases 
his  means  of  acquiring  knowledge.  It  implies  that  he  has 
a  will,  and  that  these  motive  organs  are  under  the  influence 
of  volition ;  else  he  would  be  the  sport  of  ehance  and  wan- 
der about  without  a  motive. 

2.  Many  of  the  functions  of  the  body  are  not  under  the 
control  of  the  will ;  such  are  digestion,  absorption,  circula- 
tion, respiration,  and  secretion,  which  go  on  as  well  when 
we  are  asleep  as  when  awake.  They  are  possessed,  at  least 
some  of  them,  by  vegetables  as  well  as  animals,  and  are 
therefore  called  organic  functions. 

3.  The  agents  of  locomotion  are  the  bones  and  muscles ; 
but  they  would  be  useless  for  motion  were  they  not  supplied 
with  nerves  of  voluntary  motion,  and  thus  brought  under 
the  influence  of  the  will.  The  bones  are  tied  together  by 
means  of  strong  fibrous  ligaments  or  cords,  allowing  the 
joints  great  freedom  and  extent  of  motion,  as  we  see  in  the 
shoulder  and  hip  joints. 

4.  We  then  have  the  bones,  which  act  as  levers  ;  the 
muscles  are  the  moving  power,  and  the  brain  and  nerves 
are  the  vital  agents,  which  set  the  machinery  in  motion. 
Muscles  alone  have  the  power  of  contraction,  and  it  is  one 
of  the  most  remarkable  properties  of  life.  Were  it  not  for 
this,  the  food  could  not  be  digested,  the  blood  could  not  be 


320  PHYSIOLOGY. 

circulated,  and  the  iris  could  not  guard  the  eye  against  the 
admission  of  too  much  light,  which  would  speedily  destroy 
the  vision. 

5.  The  shape  of  muscles  is  various,  some  are  round,  some 
flat,  and  the  fibres  of  which  they  are  composed,  are  con- 
nected by  means  of  cellular  membrane.  Some  are  penni- 
fbrm,  or  made  of  bundles  of  fibres,  diverging  from  a  central 
line,  like  the  feathers  of  a  quill.  Muscles  compose  a  large 
part  of  the  bulk  of  the  body  ;  and  when  they  contract,  the 
fibres  shorten  and  become  harder,  as  may  easily  be  perceived 
by  placing  one  hand  on  the  middle  of  the  arm  and  bending 
the  elbow,  or  on  the  temple  and  closing  firmly  the  lower 
jaw.    ^ 

6.  The  force  with  which  a  muscle  contracts,  depends  on 
the  physical  condition  of  the  muscle  and  the  energy  of  the 
brain.  When  the  fibres  of  the  muscle  are  large  and  firm, 
they  will  contract  with  more  force  than  when  they  are  small, 
soft,  and  delicate.  We  see  some  persons,  who  labour  under 
great  mental  excitement,  perform  astonishing  feats  of 
strength,  although,  perhaps,  they  may  not  have  muscles  of 
the  ordinary  size. 

7.  The  knee>pan  has  often  been  split  in  two  by  the  con- 
traction of  the  muscles  of  the  leg,;  a  horse  has  been  known 
to  break  its  under  jaw  by  biting  a  piece  of  iron.  Men  have 
been  known  to  lift  eight  and  nine  hundred  pounds  weight ; 
to  break  ropes  two  inches  in  circumference,  and  to  bend  a 
round  piece  of  iron,  a  yard  long,  and  three  inches  in  circum. 
ference,  to  a  right  angle,  by  striking  it  across  the  left  arm, 
between  the  shoulder  and  the  wrist,  with  the  right  hand.* 

8.  The  force  of  muscular  contraction  is  greatly  increased 
by  exercise.  The  strength  of  an  active  man  labouring  to 
the  greatest  possible  advantage,  is  estimated  to  be  sufficient 
to  raise  ten  pounds,  ten  feet  in  a  second,  for  ten  hours  in  a 
day  ;  or  to  raise  one  hundred  pounds,  one  foot  in  a  second, 

*  See  Dunglison's  Physiology. 


LOCOMOTION    AND    ITS  ORGANS.  321 

or  thirty-six  thousand  feet  in  a  day  ;  or  three  millions,  six 
hundred  thousand  pounds,  or  four  hundred  and  thirty-two 
thousand  gallons,  one  foot  in  a  day.  The  weakest  men  in 
health  can  generally  lift  about  one  hundred  and  twenty-five 
pounds,  and  the  strongest  of  ordinary  men  four  hundred 
pounds.  The  daily  work  of  a  horse  is  equal  to  that  of  five 
or  six  men. 

9.  There  is  much  difference  in  the  velocity  of  muscular 
contraction,  as  it  is  regulated  entirely  by  the  will.  The 
swiftest  race-horse  on  record  was  capable  of  going  a  mile  in 
a  minute ;  yet  this  is  trifling  compared  with  the  velocity  of 
birds,  or  even  of  many  small  insects.  It  has  been  ascer- 
tained that  a  pigeon-hawk  can  fly  one  hundred  miles  in  an 
hour  ;  the  eider-duck  ninety  miles  an  hour,  and  the  common 
crow,  twenty-five  miles  an  hour.  The  swallow  flies  ninety- 
two  miles  an  hour,  and  the  swift  is  said  to  fly  two  hundred 
and  fifty  miles  in  the  same  space  of  time. 

10.  A  falcon  belonging  to  Henry  IV.  of  France,  escaped 
from  Fontainbleau,  and  in  twenty-four  hours  after  was  in 
Malta,  a  distance  of  one  thousand  three  hundred  and  fifty 
miles,  making  a  velocity  of  fifty-seven  miles  an  hour,  sup- 
posing him  to  have  been  on  the  wing  all  the  time ;  but  as 
such  birds  do  not  fly  by  night,  his  flight  was  probably  at  the 
rate  of  seventy-five  miles  per  hour.  This  will  give  us  some 
idea  of  the  wonderful  velocity  of  the  contractions  of  the 
muscles  of  the  wings  of  birds  of  rapid  flight. 

11.  But  this  rapidity  of  motion  is  much  under  the  influ- 
ence of  habit.  How  awkward  are  the  first  attempts  at 
writing,  drawing,  dancing,  or  playing  on  musical  instru- 
ments, and  with  what  ease  and  grace  are  they  performed 
after  a  little  practice.  The  same  is  true  with  regard  to 
public  speaking,  or  any  thing  which  requires  voluntary  mo^ 
tion. 

12.  It  is  a  law  of  the  human  system,  that  relaxation  must 
follow  contraction, — or  rest,  exercise ;  and  although  the  du- 
ration  of  action  of  the  voluntary  muscles  is  in  a  great  de- 


322  PHYSIOLOGY. 

gree  under  the  control  of  the  will,  yet  it  cannot  be  continued 
long.  This  duration  will  be  shorter  in  proportion  as  the 
contraction  is  violent  or  moderate.  All  muscles  do  not  act 
at  the  same  time,  for  as  some  are  contracting,  such  as  the 
flexors,  or  those  that  bend  the  limbs,  the  extensors,  or  those 
that  straighten  them,  are  relaxed. 

13.  It  is  by  the  constant  action  of  the  muscles,  that  the 
body  is  kept  in  an  erect  position.  If  a  person  gets  asleep 
while  sitting  or  standing  up,  the  head  falls  forwards,  and  if 
he  did  not  wake,  the  body  would  fall  likewise.  The  same 
happens  when  a  person  is  deprived  of  sense,  by  a  fit  of 
apoplexy  or  palsy,  or  by  the  intemperate  use  of  ardent 
spirits. 

J 4.  We  see  that  it  requires  a  long  time  for  children  to 
learn  to  walk  securely.  The  reason  is,  that  the  base  of  sup- 
port for  the  body  is  small ;  being  only  the  space  between 
the  feet  and  that  on  which  the  feet  rest.  The  larger  the 
base,  the  easier  it  is  to  maintain  an  erect  position ;  so  that 
persons  with  small  feet  do  not  stand  as  firmly  as  those  with 
large  ones.  This  accounts  for  the  difficulty  of  standing  on 
our  toes,  or  of  walking  on  a  rope.  It  is  practice  and  in- 
stinct which  teaches  children  where  to  place  their  feet  in 
order  to  be  most  secure  when  erect ;  their  muscles  also  are 
still  weak,  for  want  of  exercise. 

15.  Walking  consists  in  a  succession  of  steps.  We  first 
balance  the  body  on  one  foot,  then  bending  the  opposite  foot 
on  the  leg,  and  the  leg  on  the  thigh,  we  bend  the  thigh  on 
the  pelvis,  and  so  shorten  the  limb.  In  this  way  the  leg  is 
brought  forward,  and  the  foot  is  then  brought  to  the  ground 
resting  first  on  the  heel ;  the  body  is  then  partially  rotated 
on  the  head  of  the  thigh  bone,  and  the  other  leg  is  raised, 
bent,  and  carried  forward  in  the  same  manner,  and  the  foot 
placed  in  advance  of  the  other.  The  legs  thus  act  as  levers 
to  propel  the  body  along,  and  the  longer  the  levers  the  more 
rapid  will  space  be  measured  over. 

16.  The  utility  of  walking  excels  that  of  all  other  modes 


LOCOMOTION    AND    ITS    ORGANS.  323 

of  progression.  While  the  able  pedestrian  is  independent 
of  stage  coaches  and  hired  horses,  he  alone  fully  enjoys  the 
scenes  through  which  he  passes,  and  is  free  to  dispose  of  his 
time  as  he  pleases.  To  counteract  these  advantages,  greater 
fatigue  is  doubtless  attendant  on  walking ;  but  this  fatigue 
is  really  the  result  of  previous  inactivity  ;  for  daily  exercise, 
gradually  increased  by  rendering  walking  more  easy  and 
agreeabJe,  and  inducing  its  more  frequent  practice,  dimi- 
nishes fatigue  in  such  a  degree,  that  very  great  distances 
may  be  accomplished  with  pleasure,  instead  of  painful  exer- 
tion. 

17.  The  power  of  walking  great  distances,  without  fa- 
tigue is  unfortunately  in  this  country  a  rare  accomplish- 
ment. A  good  walker  will  do  six  miles  an  hour,  for  one  hour, 
on  a  good  road.  If  in  good  training,  he  may  do  twelve 
miles  in  two  hours.  Eighteen  miles  in  three  hours  have 
been  achieved,  though  rarely.  At  the  rate  of  five  miles  an 
hour,  pedestrians  of  the  first  class  will  do  forty  miles  in 
eight  hours,  and  perhaps  fifty  in  ten.  Captain  Barclay 
walked  180  miles  without  resting  ;  and  also  1000  miles  in 
1000  successive  hours. 

18.  In  the  act  of  leaping,  the  whole  body  is  raised  from 
the  ground,  and  for  a  short  time  suspended  in  the  air.  It  is 
performed  by  bending  the  head  upon  the  body,  the  body  on 
the  thighs,  these  on  the  legs,  and  the  legs  on  the  feet.  The 
feet  do  not  stand  firmly  on  the  ground,  as  in  walking,  but 
the  heel  is  raised,  or  perhaps  slightly  touches  the  ground. 
The  muscles  are  all  in  a  state  of  flexion.  They  are  sudden- 
ly contracted  at  the  same  instant ;  the  consequence  is,  that 
the  feet  are  raised  from  the  ground  and  carried  forward,  and 
the  body  with  them,  until  it  is  brought  to  the  earth  by  the 
force  of  gravitation.  The  distance  passed  over,  is  in  pro- 
portion to  the  power  and  suddenness  with  which  the  muscles 
contract. 

19.  The  muscles  which  form  the  calf  of  the  leg,  act  with 
the  greatest  power  in  leaping,  as  they  have  to  raise  the  whole 


324  PHYSIOLOGY. 

body.  Their  great  strength  is  shown  by  raising  the  body 
upon  the  toes,  together  with  a  large  additional  weight ;  and 
this  power  is  not  only  owing  to  their  great  size,  but  also  to 
the  manner  in  which  they  are  inserted  into  the  heel,  thus 
having  the  advantage  of  the  long  arm  of  a  lever. 

20.  The  muscular  powers  exhibited  by  many  small  ani- 
mals and  insects  is  astonishing.  Small  animals  can  leap 
much  farther  than  large  ones,  according  to  their  size.  The 
jlea  and  the  locust  leap  two  hundred  times  their  own  length, 
as  if  a  man  should  leap  twelve  hundred  feet  high.  Others 
leap  three  hundred  times  their  length,  and  if  man  was  as 
strong  in  proportion,  he  ought  to  leap  more  than  a  quarter 
of  a  mile.  We  read  of  an  English  mechanic,  who  made  a 
golden  chain  as  long  as  the  finger,  with  a  lock  and  key, 
which  was  dragged  by  a  flea,  and  of  another  flea  dragging 
a  silver  cannon  on  wheels,  that  was  twenty-four  times  its 
own  weight.  This  cannon  was  charged  with  powder  and 
fired  without  the  flea  seeming  to  be  alarmed.  A  cockroach, 
or  an  ant  is  six  times  as  strong,  for  its  size,  as  a  horse  ;  and, 
if  an  elephant  were  as  strong  in  proportion,  he  would  be 
able  to  tear  up  rocks  and  level  mountains. 

21.  Hopping  is  merely  leaping  on  one  foot.  As  but  half 
the  muscular  power  is  exerted,  a  man  ought  to  be  able  to 
leap  twice  as  far  as  he  can  hop.  Running  consists  of  a 
succession  of  low  leaps,  performed  by  each  leg  alternately. 
It  differs  from  walking,  in  the  body  being  thrown  forward  at 
each  step,  and  the  hind  foot  being  raised  before  the  fore  foot 
touches  the  ground.  A  person  cannot  stop  running  instant- 
ly, as  he  can  walking,  because  his  velocity  is  so  great  as  to 
carry  him  forward  a  certain  distance,  whether  he  uses  his 
muscles  or  not,  and  thus  occasions  him  to  fall. 

22.  The  practice  of  running  may  be  carried  to  a  great 
degree  of  perfection.  A  quarter  of  a  mile  in  a  minute  is 
good  running ;  and  a  mile  in  four  minutes,  at  four  starts,  is 
excellent.  A  mile  was  perhaps  never  run  in  four  minutes ; 
but  it  has  been  done  in  four  minutes  and  a  half.     A  mile  in 


LOCOMOTION    AND    ITS    ORGANS.  325 

five  minutes  is  called  very  good  running ;  two  miles  in  teil 
minutes  is  but  rarely  accomplished.  Ten  miles  an  hour  is 
done  by  all  the  best  runners.  Forty  miles,  in  four  hours 
and  three  quarters  has  been  done  by  one  individual.  Some 
Indians,  it  is  said,  will  run  at  this  rate  for  several  hours,  but 
it  is  very  doubtful. 

23.  Swimming  is  very  much  like  leaping  ;  at  least  the 
same  muscles  are  brought  into  action  in  the  lower  limbs. 
While  the  hands  are  brought  to  a  point  before  the  head,  the 
legs  are  drawn  up  and  suddenly  extended,  as  in  leaping.  By 
the  resistance  of  the  water,  the  body  is  projected  forwards. 
The  hands  are  now  carried,  with  a  circular  motion,  the 
palms  being  turned  outwards,  till  they  reach  the  sides  of  the 
body,  and  thus  the  impulse  through  the  water  is  kept  up  by 
a  constant  succession  of  these  movements.  A  boat  is  pro- 
pelled on  the  same  principle.  Indeed  the  body  may  be  com- 
pared to  the  boat  itself,  and  the  hands  and  feet  to  the  oars. 
A  good  swimmer  ought  to  make  three  miles  an  hour. 

24.  The  human  body  is  very  nearly  of  the  same  specific 
gravity  as  water ;  that  is,  it  is  of  the  same  weight  as  a  body 
of  water  of  the  same  bulk.  Dr.  Franklin  says  if  a  person 
avoids  struggling  and  plunging,  he  may  lie  on  his  back  with 
his  mouth  and  face  out  of  water,  without  difficulty,  even  if 
he  cannot  swim.  As  swimming  therefore,  is  a  highly  useful 
art,  and  an  agreeable  and  healthy  exercise,  it  should  be  made 
a  necessary  part  of  the  education  of  boys. 

25.  The  importance  of  gymnastic  exercises  will  only  be 
questioned  by  those  who  are  not  aware  that  the  health  and 
vigour  of  all  the  bodily  organs  depend  on  the  proportioned 
exercise  of  each.  Such  exercises  ensure  the  development 
of  all  the  locomotive  organs ;  and  they  prevent  or  correct 
all  the  deformities  to  which  those  organs  are  liable.  They 
are  the  best  calculated  to  produce  strength  and  activity,  and 
to  bestow  invariable  health.  At  the  same  time  they  confer 
beauty  of  form,  and  contribute  to  impart  an  elegant  air  and 
graceful  manners. 

28 


CHAPTER  XXVII. 


THE   TEETH. 


1.  As  the  teeth  are  the  only  bones  in  the  human  frame 
which  are  exposed  to  the  immediate  action  of  foreign  bodies^ 
they  merit  distinct  and  special  consideration  in  this  treatise 
on  the  General  Physiology  of  man.  The  most  remarkable 
fact  in  their  history  is,  that  unlike  the  other  bones,  the  teeth 
which  make  their  appearance  in  infancy,  are  removed  at  the 
age  of  seven  or  thereabouts,  and  another  set  come  forward 
to  supply  their  places. 

2.  The  first  set  called  temporary  teeth,  are  just  twenty  in 
number,  ten  in  each  jaw.  The  two  front  teeth  above  and  be- 
low, are  known  as  central  incisors,  because  they  serve  to  cut 
the  food.  The  teeth  adjoining  these  are  denominated  lateral 
incisors,  next  to  which  come  the  canine  or  dog  teeth,  of 
which  those  in  the  upper  jaw  are  called  eye  teeth.  Back  of 
these  at  either  extremity  of  each  dental  arch  are  two  larger 
teeth  known  as  grinders  from  the  fact  that  they  operate  like 
mill-stones,  in  reducing  the  food  to  very  minute  particles  in 
preparation  for  quick  and  easy  digestion. 

3.  The  second  or  permanent  set  has  twelve  additional 
teeth,  six  above  and  six  below,  making  thirty. two  in  all. 
The  two  next  back  of  each  eye  tooth,  are  styled  bicuspids, 
because  they  terminate  in  two  points  ;  and  the  four  extreme 
grinders  are  sometimes  called  vnsdom  teeth,  because  they  do 
not  generally  appear  until  the  individual  arrives  at  mature 
age.  Thus,  there  are  twelve  grinders  or  molar  teeth  in  the 
second  set  instead  of  eight  as  in  the  first  set ;  and  there  are 
eight  bicuspids  which  are  not  found  among  the  temporary 
teeth  at  all. 

4.  Each  tooth  consists  of  two  distinct  parts,  called  the 
crovm  and  root ;  the  former  being  that  portion  which  pro- 


THE    TEETH.  327 

jects  from  the  gum  into  the  cavity  of  the  mouth,  and  the  lat. 
ter  that  which  is  buried  in  the  socket.  The  incisors,  eye 
teeth  and  bicuspids  have  one  root  each,  the  upper  grinders 
three  and  the  lower  grinders  two.  The  roots  of  the  wisdom 
teeth  are  commonly  compressed  into  one  mass  having  little 
or  no  divergency,  and  in  rare  instances  the  bicuspids  have 
two  distinct  fangs,  while  the  upper  molars  have  been  known 
to  have  four  or  five  distinct  roots. 

5.  Every  human  tooth  is  composed  of  two  distinctly  or- 
ganised substances,  namely  the  enamel  covering  the  crown, 
and  the  osseous  or  bony  portion  which  constitutes  the  re- 
remainder  of  the  tooth.  The  osseous  part  is  scarcely  distin- 
guishable from  other  bony  structures  excepting  from  its 
greater  density.  The  enamel  on  the  contrary,  is  remarka- 
ble for  its  extreme  hardness  resulting  from  its  chrystaline 
structure.  It  consists  of  needle-formed  crystals,  one  ex- 
tremity of  which  rests  upon  the  bone  beneath,  while  the 
other  is  presented  to  the  food. 

6.  The  teeth  are  found  by  chemical  analysis  to  consist  of 
nearly  the  same  elementary  substances  as  the  other  bones  ; 
namely,  phosphorus,  lime,  magnesia,  soda,  carbon,  oxygen, 
chlorine,  gelatine  and  water.  As  the  teeth  are  a  part  of  the 
living  system,  they  are  supplied  with  nerves,  blood  vessels 
and  absorbents,  not  only  by  a  central  cavity  extending  from 
the  point  of  each  root  to  the  middle  of  the  crown,  but  by  a 
membranous  sheath  enveloping  the  root  called  the  periosteum, 
as  is  true  of  the  other  bones. 

7.  The  teeth  are  firmly  attached  to  the  jaw  or  maxillary 
bone,  by  means  of  sockets  called  alveoli.  In  case  of  extrac- 
tion the  alveoli  yield  to  moderate  pressure  and  sufTer  the 
teeth  to  escape  without  any  injury  to  the  adjacent  parts  ; 
and  as  soon  as  the  teeth  are  removed  the  investigating  bone 
is  sufficient  to  produce  immediate  absorbtion. 

8.  The  first  set  of  teeth  begin  to  make  their  appearance 
through  the  gums,  between  the  sixth  and  eighth  month,  and 
before  the  infant  arrives  at  the  thirtieth  month  all  the  teeth 


328  PHYSIOLOGY. 

have  assumed  their  natural  position.  The  second  dentition 
commences  about  the  seventh  year,  and  is  commonly  per- 
fected before  the  fourteenth. 

9.  When  the  teeth  are  so  much  crowded  as  to  disturb 
their  regular  arrangement ;  or  when  they  press  so  hard  upon 
each  other  as  to  destroy  the  enamel,  one  or  more  should  be 
removed  without  delay.  If  this  precaution  should  be  ne- 
glected, an  unsightly  mal-arrangement,  or  inevitable  destruc- 
tion of  several  of  the  teeth,  will  be  the  melancholy  result. 
The  removal  of  a  sound  tooth  causes  very  little  pain  com- 
pared with  the  agony  attending  those  which  are  suffered  to 
become  diseased. 

10.  It  is  impossible,  under  ordinary  circumstances,  to 
preserve  the  teeth  for  many  years  without  keeping  them 
very  clean.  Food  lodges  between  them  at  every  meal,  and 
undergoes  decomposition  if  not  removed.  A  substance,  called 
tartar,  or  salivary  calculus,  which  is  deposited  from  the 
saliva,  adheres  to  the  teeth,  becomes  very  hard,  and  finally 
assumes  a  dark  colour,  if  not  constantly  washed  away  with 
a  brush  and  water.  If  food  be  suffered  to  putrefy  in  spaces 
between  the  teeth  the  process  of  mortification  is  extended  to 
the  teeth  themselves ;  and  if  tartar  collect  in  solid  masses, 
the  teeth  become  loose  in  their  sockets  and  are  thus  utterly 
tost. 

11.  In  order  to  keep  the  teeth  and  gums  perfectly  clean 
and  healthy,  it  is  necessary  to  wash  them  with  a  stiff  brush 
and  water  several  times  in  a  day.  No  person  of  ordinary 
neatness  would  consent  to  eat  with  knives,  forks  and  spoons, 
unless  they  were  cleansed  after  every  meal.  The  teeth  are 
more  liable  to  accumulate  filth  than  any  of  these  domestic 
utensils,  and  therefore  need  at  least  equally  frequent  washing. 
In  the  morning,  after  each  meal,  and  before  retiring  to  rest, 
are  not  too  many  times  to  purify  the  teeth  with  a  brush  and 
water,  and  once  in  each  week  with  good  tooth  powder. 

12r.  The  Dentifrice  or  Tooth  Powder,  which  I  would  re- 
eomraend  in  preference  to  all  others  which  I  have  ever  seeaj 


THE    TEETH.  329 

is  composed  of  the  following  ingredients,  well  pulverised  in 
a  mortar,  and  intimately  mixed  together : 

Loaf  sugar,  half  an  ounce, 

Cinnamon,  half  an  ounce, 

Gum  Kino,  quarter  of  an  ounce, 

Peruvian  bark,  three  ounces. 

Prepared  chalk,  six  ounces, 

Armenian  Bole,  five  and  a  half  ounces ; 
making  one  pound  avoirdupoise. 

13.  In  addition  to  the  above  described  dentifrice,  every 
person  should  be  provided  with  a  good  tooth  brush,  which 
should  be  laid  aside  as  useless  whenever  it  loses  its  stiffness 
and  elasticity.  A  piece  of  gloss-silk,  well  waxed,  should  be 
employed  to  cleanse  the  open  spaces  between  the  teeth,  inas- 
much as  these  are  not  easily  cleansed  with  the  brush  alone. 
If  tooth-picks  are  used  at  all,  they  should  be  made  of  wood 
or  quill,  since  those  formed  of  any  of  the  metals,  particularly 
of  steel  or  iron,  are  quite  too  hard,  and  therefore  destructive 
to  the  teeth  and  gums. 

14.  If  brushing  the  teeth  and  using  the  other  methods  of 
keeping  them  in  order  as  above  described,  should  fail  of 
effecting  the  desired  purpose,  the  assistance  of  the  dentist 
should  be  put  in  requisition.  With  his  scaling  instruments, 
he  can  effectually  remove  every  vestige  of  tartar,  together 
with  any  other  impurities  lodged  upon  the  teeth.  Above  all, 
abstain  from  the  use  of  all  kinds  of  powders  and  washes 
which  render  the  teeth  white  by  chemical  action.  These 
contain  acid  in  one  form  or  another,  and  are  therefore  de* 
structive  to  the  teeth. 

15.  Persons  desirous  of  preserving  their  teeth  in  a  sound 
and  healthy  state  for  many  years,  should  consult  their  gene* 
ral  health  in  all  their  habits  of  life,  especially  in  relation  to 
food  and  drinks.  Neither  solid  nor  fluid  aliment  should  be 
taken  into  the  mouth  at  either  very  high  or  very  low  tem^ 
perature,  because  sudden  transitions  from  heat  to  cold,  or 
from  cold  to  heat,  are  liable  to  crack  the  enamel  of  the  teetU 

88* 


330  PHYSIOLOGY. 

by  unequal  expansion  and  contraction,  as  is  readily  ascer- 
tained by  the  assistance  of  the  microscope.  Teeth  thua 
injured,  almost  always  decay  in  consequence  of  the  exposure 
of  the  bony  substance  of  the  tooth  to  the  action  of  corro- 
sive fluids. 

16.  There  are  three  prevalent  general  causes  of  the  de- 
struction of  human  teeth,  besides  occasional  accident :  viz. 
accumulation  of  tartar,  ulceration  of  the  fangs,  and  dental 
gangrene.  Ulcers  of  the  fangs  extend  to  the  alveoli  or 
sockets,  which  are  also  destroyed,  together  with  the  invest- 
ing gum.  The  well  informed  dentist  can  best  prescribe  and 
apply  the  proper  remedies  for  all  these  forms  of  dental  dis- 
ease. 


,  CHAPTER  XXVIII. 

SLEEP    AND    DEATH. 

1.  Sleep  is  the  periodical  and  temporary  suspension  of 
those  functions  that  connect  us  with  the  external  world* 
Man  is  so  constituted,  that  the  functions  of  sensibility,  vol- 
untary motion,  and  the  intellectual  faculties  cannot  be  in- 
dulged for  any  length  of  time  without  fatigue.  The  nervous 
energy,  which  seems  essential  to  their  exercise,  becomes  ex- 
hausted ;  the  muscles  can  no  longer  contract ;  the  external 
senses  cannot  receive  impressions ;  the  brain,  and  conse- 
quently the  mind,  becomes  torpid  ;  and  a  person  sinks  into 
a  state  of  torpor  and  inaction,  called  sleep. 

2.  The  approach  of  sleep  is  announced  by  an  internal 
sensation,  termed  drowsiness,  which  gradually  increases  in 
strength,  till  at  length  it  becomes  irresistible.  Great  languor 
of  the  muscles  and  heaviness  of  the  eyes  are  experienced ; 
the  sight  yields  first ;  next  the  smell ;  then  the  hearing  ;  and 
lastly,  the  sense  of  touch  ;  while  at  the  same  time,  all  the 
internal  sensations,  such  as  hunger  and  thirst,  are  no  longer 
felt.  The  will  ceases  to  control  the  functions  that  are  under 
its  influence,  till  finally  all  power  of  volition  is  wholly  lost. 
Respiration  is  still  carried  on^  but  chiefly  by  means  of  the 
diaphragm,  which  is  an  involuntary  muscle ;  it  is,  however, 
somewhat  slower,  as  well  as  the  circulation,  than  in  the 
waking  condition. 

3.  During  perfect  sleep,  the  functions  of  the  brain  are  en- 
tirely suspended.  In  such  a  state,  dreams  do  not  happen  ; 
for  as  the  brain  is  in  a  state  of  complete  inaction,  the  intel- 
lectual operations  are  consequently  dormant.  When  the 
brain  is  not  in  a  state  of  complete  repose,  objects  and  images 
may  float  confusedly  through  the  mind,  which  are  often  the 
result  of  external  impressions  imperfectly  perceived,  as  they 
eixcite  but  an  imperfect  reaction  in  the  brain^ 


332  PHYSIOLOGY. 

4.  The  organic  or  nutritial  functions  continue  during 
sleep,  but  with  diminished  energy.  The  circulation  and 
respiration  are  not  only  slower,  but  digestion  is  retarded, 
and  secretion,  nutrition,  and  calorification,  are  less  active 
than  when  awake.  The  temperature  of  the  body  is  also 
lowered  during  sleep,  which  may  perhaps  be  owing  to  the 
facts  above  mentioned. 

5.  The  duration  of  sleep  is  influenced  by  a  variety  of 
circumstances.  The  average  time  of  regular,  periodical 
sleep,  in  adults,  is  from  five  to  eight  hours.  Infants  require 
twice  as  much  sleep  as  grown  persons.  The  quantity  of 
sleep  required,  depends  very  much  upon  habit.  It  is  said  of 
Pichegru,  one  of  Buonaparte's  generals,  that,  for  a  whole 
year,  he  had  not  more  than  one  hour  of  sleep  in  twenty-four 
hours.  Buonaparte  himself,  when  on  active  duty,  seldom 
slept  more  than  three  hours  in  twenty-four ;  often  but  one 
hour.  Men  of  active  minds,  who  are  engaged  in  a  series 
of  interesting  employments,  sleep  much  less  than  the  lazy 
and  the  listless.  The  intellectual  and  moral  faculties  seem 
to  require  a  longer  period  of  repose  than  the  functions  of 
voluntary  motion. 

6.  Though  the  night  is  the  proper  season  for  sleep,  owing 
to  the  absence  of  light,  diminished  warmth,  its  comparative 
stillness,  as  well  as  the  exhaustion  caused  by  the  labours  of 
the  day,  yet  some  animals,  which  pursue  their  prey  by  night, 
sleep  during  the  day,  as  the  cat,  fox,  wolf,  otter,  owl,  and 
bat.  Hybernating  animals  sleep  for  several  months  during 
the  winter,  such  as  the  bear,  hedge-hog,  marmot,  &;c.  Some 
birds,  also,  such  as  bats  and  swallows,  sleep  during  the  win. 
ter,  or  hybernate.  During  this  state  their  temperature  is  di- 
minished, their  secretions  nearly  checked,  their  excretions 
suppressed,  their  respiration  slow,  and  scarcely  perceptible, 
their  circulation  very  languid,  and  sensibility  to  external  im- 
pressions entirely  suspended.  The  arterial  blood  of  hyber- 
nating animals,  diiOfers  but  little  from  venous  blood. 

7.  Dreams  are   now  considered  by  physiologists  to  be 


SLEEP    AND    DEATH.  333 

owing  to  an  irregular  action  of  the  brain,  in  which  the  con- 
trolHng  power  of  the  will  is  lost,  and  the  memory  and  the 
imagination  bear  unlimited  sway.  Indeed  all  the  faculties 
of  the  mind  may  be  in  exercise.  The  mind  reasons,  judges, 
wills,  and  experiences  all  the  various  emotions.  We  seem 
to  hear,  see,  walk,  talk,  and  perform  the  usual  offices  of  life. 
Sometimes  the  voluntary  muscles  are  thrown  into  action, 
and  the  dreamer  moves,  speaks,  groans,  cries,  or  sings ;  but 
the  moment  consciousness  is  roused,  he  is  awake.  Dreams, 
therefore,  have  well  been  said  to  be  "  a  portion  of  animal 
life,  escaping  from  the  torpor  in  which  the  rest  of  it  lies 
buried." 

8.  Before  the  functions  of  the  brain  were  understood, 
dreams  were  regarded  as  supernatural,  and  even  now  are 
considered  in  this  light  by  the  ignorant  and  superstitious. 
Mr.  Baxter,  as  well  as  Bishop  Newton  divided  them  into  two 
kinds,  good  and  evil,  because  they  believed  that  good  and 
evil  spirits  were  concerned  in  their  production,  according  as 
one  or  the  other  obtained  the  ascendancy.  It  is  supposed 
that  animals  dream,  especially  the  dog ;  are  they  subject  to 
supernatural  influence  1 

9.  It  is  a  singular  circumstance  in  relation  to  our  dreams, 
that  we  mistake  our  ideas  for  actual  perceptions,  and  sup- 
pose that  the  train  of  images  that  passes  through  our  minds, 
represents  scenes  which  really  exist.  This  is  doubtless  owing 
to  the  fact  that,  during  sleep,  the  senses  do  not  admit  exter- 
nal impressions,  and  of  course  we  are  unable  to  compare  the 
ideas  that  arise  in  our  minds  with  sensible  impressions,  and 
thus  perceive  the  difference  between  them.  Our  only  con- 
sciousness consists  in  the  images  and  ideas  actually  present 
in  the  mind ;  and  it  is  therefore  unavoidable  that  we  should 
believe  that  our  ideas  represent  objects  actually  existing. 

10.  There  is  a  kind  of  dreaming,  in  some  cases  of  imper- 
fect sleep,  where  the  will  retains  its  power  over  the  muscles 
of  voluntary  motion,  while  the  external  senses  remain  buried 


334  PHYSIOLOGY. 

in  partial  or  complete  repose.     This  is  called  somnambulism 
or  sleep-walking, 

11.  Many  remarkable  cases  of  somnambulism  have  been 
lately  published,  as  the  effects  of  animal  magnetism ;  but  in 
many  of  these,  it  is  to  be  feared,  credulity  existed  on  one 
side,  and  imposition  was  practised  on  the  other.  That  som- 
nambulism, or  a  state  nearly  similar,  is  brought  about  by  the 
practices  of  magnetizers  in  persons  of  acute  sensibility,  and 
highly  excitable  nervous  temperament,  would  seem  scarcely 
to  admit  of  a  doubt.  Still,  all  such  cases  should  be  regarded 
with  great  circumspection,  and  every  means  employed  to 
detect  imposition  and  fraud. 

12.  Somnambulism  seems  to  differ  from  the  waking  state, 
only  in  consciousness  being  absent.  The  person  appears  to 
enjoy  the  full  exercise  of  all  his  faculties  ;  he  can  converse, 
walk,  sing,  compose  verses,  and  perform  various  operations  ; 
and  yet  in  the  waking  state  he  has  no  recollection  of  what 
has  occurred.  In  this  respect  somnambulism  differs  from 
dreaming,  and  resembles  a  morbid  state ;  indeed,  it  is  a  state 
of  disease  analagous  to  trance,  catalepsy,  or  epilepsy. 

13.  A  state,  the  reverse  of  somnambulism,  is  called  incu- 
bus, or  nightmare.  In  this  affection,  a  person  feels  a  sense 
of  weight  and  suffocation,  as  if  there  was  a  heavy  load  on 
his  stomach  or  chest,  and  imagines  that  some  frightful  object 
is  seated  there.  This  is  owing  to  some  oppression  of  the 
digestive,  circulatory,  and  respiratory  organs,  most  usually 
occasioned  by  a  late,  hearty  supper  of  indigestible  food. 
Frightful  dreams  denote  ill  health,  and  are  often  caused  by 
a  derangement  of  some  important  organ,  as  of  the  heart, 
stomach,  or  liver,  exciting  the  brain  to  sympathetic  action. 
To  dream  immediately  on  going  to  sleep,  is  always  a  mark 
of  disease. 

14.  There  is  still  another  state  which  bears  a  close  resera- 
blance  to  somnambulism,  and  this  is  termed  revery,  absence 
of  mind,  or  broum  study.     In  this,  the  attention  is  so  com- 


SLEEP    AND    DEATH.  335 

pletely  riveted  to  some  particular  subject,  that  the  person  is 
entirely  insensible  to  the  presence  of  surrounding  objects. 

15.  One  great  object  of  education  is  to  give  the  will  power 
over  the  attention.  The  mind  that  cannot  command  this 
faculty,  is  in  a  deplorable  condition  for  all  the  higher  pur- 
poses of  reflection  and  knowledge  for  which  it  is  intended. 
Without  it,  perception  exercises  itself  in  vain  ;  the  memory 
can  lay  up  no  store  of  ideas ;  the  judgment  draw  forth  no 
comparisons  ;  the  imagination  must  become  blighted  and 
barren ;  and  in  proportion  as  a  person  has  no  command 
over  his  attention,  in  that  degree  must  he  be  an  idiot. 

16.  It  is  the  will  of  Providence  that  all  organized  beings 
must  perish.  For  a  while,  life  maintains  a  successful  con- 
flict with  the  chemical  laws  of  matter  ;  but  at  length  its  re- 
sistance becomes  weaker  and  weaker,  till,  sooner  or  later, 
those  functions  cease  which  have  enabled  us  to  withstand 
the  destructive  influences  by  which  we  are  surrounded. 

17.  The  duration  of  life  varies,  not  only  in  the  animal  but 
in  the  vegetable  kingdom.  As  a  general  rule,  where  the 
growth  is  slow,  the  period  of  decrease  is  proportionably 
slow ;  and  where  it  is  rapid,  decay  as  rapidly  supervenes. 
The  gourd  that  sprang  up  in  a  night,  perished  also  in  a 
night. 

18.  There  are  two  kinds  of  death,  natural  and  accidental. 
Natural  death,  or  that  of  old  age,  is  caused  by  a  gradual 
decay  and  wearing  out  of  all  the  organs  ;  accidental  death, 
or  such  as  is  occasioned  by  accident,  cuts  off*  existence  pre- 
maturely. The  natural  period  of  life  differs  in  different 
individuals  ;  being  influenced  by  a  variety  of  circumstances ; 
such  as  the  original  constitution ;  habits  of  life  ;  and  the 
health  of  the  locality  where  a  person  is  situated. 

19.  The  natural  period  of  life,  has  not  materially  diflJered 
since  the  time  of  the  flood.  «  The  days  of  our  years,"  says 
the  Psalmist,  "  are  threescore  and  ten  ;  and  if  by  reason  of 
strength  they  be  fourscore  years,  yet  is  their  strength  labour 
and  sorrow,  for  it  is  soon  cut  off*  and  we  fly  away."     This 


386  PHYSIOLOGY. 

description  is  as  applicable  now,  as  it  was  four  thousand 
years  ago. 

20.  Those  who  die  from  old  age  are  few ;  being,  in  the 
city  of  New  York,  but  one  in  thirty-four.  In  New  En- 
gland, generally,  the  proportion  is  rather  greater.  The 
mean  duration  of  life  in  New  York  is  but  twenty-five  years  ; 
while  the  average  rate  of  mortality,  according  to  population, 
is  one  in  thirty-five.  The  diseases  to  which  man  is  subject, 
from  the  earliest  to  the  latest  period  of  his  existence,  are 
numerous,  and  many  of  them  of  a  fatal  character.  Syden- 
ham estimates  that  two  thirds  of  mankind  die  of  acute  dis- 
eases ;  and  that  of  the  remaining,  one  third,  or  two  ninths 
of  the  whole,  die  of  consumption,  leaving  only  one  ninth  to 
perish  from  other  chronic  maladies,  and  from  pure  old  age. 

20.  As  age  approaches,  the  functions  are  all  performed 
with  less  energy.  The  teeth  fall  out,  and  their  sockets  are 
absorbed  ;  respiration  is  not  as  readily  accomplished ;  the 
valves  of  the  heart,  and  the  coats  of  many  of  the  arteries 
become  changed  into  bone,  thus  obstructing  the  circulation, 
and  often  causing  an  intermittent  pulse ;  nutrition  lan- 
guishes ;  the  senses  are  blunted  ;  animal  heat  diminishes,  so 
that  warmer  clothing  is  demanded  ;  the  muscular  system 
loses  its  power,  and  the  body  bends  forward  ;  the  limbs  totter, 
the  mental  as  well  as  corporeal  faculties  often  fail ;  and  the 
individual  is  reduced  to  second  childhood,  so  well  described 
by  Shakspeare. 

"  Last  scene  of  all, 
That  ends  this  strange,  eventful  history, 
Is  second  childishness,  and   mere  oblivion  ; 
Sans  teeth,  Sans  eyes,  Sans  taste.  Sans  everything.'* 

As  the  other  functions  cease  their  office,  sensibility  gradual- 
ly becomes  e^i]^,  ^nd^jl^fe  almost  imperceptibly  takes  its 

flight,  ^^^o^'^'^rj^.. 


mK 


•h-..^^-»V«^ 


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Human  physiolol 


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^KH         Ot  *.^"' 


